Shao Quan Liu

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Organization: National University of Singapore , Singapore

Department: Department of Chemistry

Title: (PhD)

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Applied Chemistry

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Chemicals
References

Chemical consequences of three commercial strains of Oenococcus oeni co-inoculated with Torulaspora delbrueckii in durian wine fermentation

Co-reporter:Yuyun Lu, Jian-Yong Chua, Dejian Huang, Pin-Rou Lee, Shao-Quan Liu

Food Chemistry 2017 Volume 215() pp:209-218

Publication Date(Web):15 January 2017

DOI:10.1016/j.foodchem.2016.07.158

•O. oeni strains were co-inoculated with Torulaspora delbrueckii in durian wine.•O. oeni caused early death of T. delbrueckii.•O. oeni significantly affected some organic acid metabolism.•Malolactic fermentation altered volatile profiles in durian wine.This work evaluated for the first time the chemical consequences of three commercial strains of Oenococcus oeni co-inoculated with Torulaspora delbrueckii in durian wine fermentation. Compared with the control (yeast only, 5.70% v/v ethanol produced), samples co-inoculated with T. delbrueckii and O. oeni PN4 improved ethanol production (6.06% v/v), which was significantly higher than samples co-inoculated with Viniflora (4.78% v/v) or Enoferm Beta (5.01% v/v). Wines co-fermented with the respective latter two oenococci contained excessive levels of ethyl acetate (>80 mg/L) that were likely to affect negatively wine aroma. In addition, they led to significantly higher acetic and lactic acid production relative to PN4. O. oeni PN4 seemed to be the most suitable strain to co-inoculate with T. delbrueckii for simultaneous alcoholic and malolactic fermentation in durian wine by contributing moderately increased concentrations of higher alcohols, acetate esters and ethyl esters that would have positive sensory impacts.

Effects of sucrose monopalmitate (P90), Tween 80 and modified starch on coffee aroma retention and release in coffee oil-based emulsions

Co-reporter:Liang Wei Lee, Xuesi Liu, Wai San Elsa Wong, Shao Quan Liu

Food Hydrocolloids 2017 Volume 66(Volume 66) pp:

Publication Date(Web):1 May 2017

DOI:10.1016/j.foodhyd.2016.12.021

•The use of nano-emulsions was explored for the enrichment of instant coffee aroma.•Volatiles levels in emulsion matrices were significantly lower compared to control.•Volatiles retention was observed in P90-stabilized emulsion after freeze-drying.•Spiking P90-stabilized emulsion into instant coffee raised its total volatile level.•The extent of volatiles retention and release varied with the type of emulsifier.Despite the convenience and extended shelf life of instant coffee, its aroma profile is less desirable compared to freshly brewed coffee. The objective of this study was to evaluate the effects of sucrose monopalmitate (P90), modified starch (MS) and Tween 80 on coffee aroma retention and release in oil-in-water emulsion matrices (coffee oil as the flavor matrix) and upon spiking into instant coffee, with an aim to enrich instant coffee aroma. The volatile profiles of P90-, MS- and Tween 80-stabilized coffee emulsions before, after freeze-drying and upon spiking into instant coffee were characterized with HS-SPME-GC-MS/FID and compared. The extent of volatile retention and release varied with the type of emulsifiers and volatile classes. Aldehydes and phenolic compounds levels in P90-stabilized coffee emulsions were 40% and 30% significantly lower compared to the control while their levels in Tween 80-stabilized coffee emulsion were 8% and 38% lower compared to the control respectively. Phenolic compounds levels in MS-stabilized coffee emulsion were 13% significantly lower compared to the control. Volatile retention remained after freeze-drying for P90- and Tween 80-stabilized coffee emulsions where total volatile levels were 12% and 25% significantly lower compared to the controls, respectively. The total volatiles levels of instant coffees spiked with P90- and MS-stabilized coffee emulsions were higher compared to the blank and spiking with the controls. The trend was reversed when Tween 80-stabilized coffee emulsion was spiked. Therefore, P90- and MS-stabilized coffee emulsions exhibited some extent of controlled aroma release and could be utilized for instant coffee aroma enrichment.Download high-res image (201KB)Download full-size image

Pentopan mono BG pretreatment of palm kernels modified the aroma of palm kernel oil after kernel roasting

Co-reporter:Wencan Zhang, Feifei Zhao, Fangju Zhao, Tiankui Yang, Shaoquan Liu

LWT - Food Science and Technology 2017 Volume 86(Volume 86) pp:

Publication Date(Web):1 December 2017

DOI:10.1016/j.lwt.2017.08.055

•A 1.3-fold increment of total soluble sugars was found after Pentopan treatment.•Obvious increments of O-heterocyclic compounds were found in treated PKO.•Elevation in furfural and 2-furanmethanol was most evident in treated PKO.•Treated PKO (medium roast) rendered a more nutty, smoky and caramelic odor.With an interest to enhance the aroma of palm kernel oil (PKO), Pentopan mono BG (xylanase) was applied to alter the carbohydrates in palm kernels (PK) so as to modulate the formation of volatiles during kernel roasting. The result showed that a 1.3-fold increment of total soluble sugars was found in PK after Pentopan treatment, which promoted the generation of O-heterocyclic volatile compounds during kernel roasting. Overall, an increment of 1.5-, 1.4- and 1.3-fold of O-heterocyclic compounds were found in PKO derived from treated PK after light, medium and dark roasting, of which the elevation in furfural and 2-furanmethanol contents was the most obvious. Principal component analysis (PCA) clearly discriminated treated PKO with various kernel roasting degrees from that of control PKO on the basis of all aroma-active compounds; the aroma in PKO from treated, roasted PK was highly correlated with 2-[(methyldithio)methyl]-furan, 5-methyl-2-furancarboxaldehyde, 2-furanmethanol, 2,5-dimethylpyrazine and ethyl pyrazine. Sensory evaluation showed that PKO derived from medium roasted PK imparted more caramelic, nutty and smoky odor notes relative to the untreated PKO. This study suggests Pentopan pretreatment of PK followed by roasting may be a novel way to modulate PKO aroma and potentially widen its application.

Combined effects of fermentation temperature and pH on kinetic changes of chemical constituents of durian wine fermented with Saccharomyces cerevisiae

Co-reporter:Yuyun Lu;Marilyn Kai Wen Voon;Dejian Huang

Applied Microbiology and Biotechnology 2017 Volume 101( Issue 7) pp:3005-3014

Publication Date(Web):12 December 2016

DOI:10.1007/s00253-016-8043-1

This study investigated the effects of temperature (20 and 30 °C) and pH (pH 3.1, 3.9) on kinetic changes of chemical constituents of the durian wine fermented with Saccharomyces cerevisiae. Temperature significantly affected growth of S. cerevisiae EC-1118 regardless of pH with a higher temperature leading to a faster cell death. The pH had a more significant effect on ethanol production than temperature with higher production at 20 °C (5.95%, v/v) and 30 °C (5.56%, v/v) at pH 3.9, relative to that at pH 3.1 (5.25 and 5.01%, v/v). However, relatively higher levels of isobutyl alcohol and isoamyl alcohol up to 64.52 ± 6.39 and 56.27 ± 3.00 mg/L, respectively, were produced at pH 3.1 than at pH 3.9 regardless of temperature. In contrast, production of esters was more affected by temperature than pH, where levels of ethyl esters (ethyl esters of octanoate, nonanoate, and decanoate) and acetate esters (ethyl acetate and isoamyl acetate) were significantly higher up to 2.13 ± 0.23 and 4.61 ± 0.22 mg/L, respectively, at 20 °C than at 30 °C. On the other hand, higher temperature improved the reduction of volatile sulfur compounds. This study illustrated that temperature control would be a more effective tool than pH in modulating the resulting aroma compound profile of durian wine.

Modulation of the volatile and non-volatile profiles of coffee fermented with Yarrowia lipolytica: I. Green coffee

Co-reporter:Liang Wei Lee, Geng Yu Tay, Mun Wai Cheong, Philip Curran, Bin Yu, Shao Quan Liu

LWT - Food Science and Technology 2017 Volume 77(Volume 77) pp:

Publication Date(Web):1 April 2017

DOI:10.1016/j.lwt.2016.11.047

•Green coffee beans were fermented with a food yeast Yarrowia lipolytica.•Y. lipolytica fermentation modified coffee aroma precursors.•Significant decreases in amino and phenolic acids concentrations were observed.•Phenolic acids metabolism contributed to the increase in volatile phenols levels.•Significant decreases in volatile acids, aldehydes and alkanes levels were detected.Yeast starter cultures have been used in the fermentation of different coffee substrates to modulate the volatile and aroma profiles of coffees with the exception of green coffee beans. This two-part study aimed to modulate the volatile profiles of roasted coffee via the fermentation of green coffee beans with a non-conventional aerobic yeast Yarrowia lipolytica. The objective of part I of this study was to evaluate the effects of Y. lipolytica fermentation on the volatile and non-volatile profiles of green coffee beans. After fermentation, sugars concentration decreased by 1.2-fold while the amino and phenolic acids concentrations decreased by 1.3-fold. The decrease in phenolic acid concentration could account for the 1.5-fold increase in the volatile phenols levels resulting from phenolic acid catabolism. The degradation of l-phenylalanine via the Ehrlich pathway by the yeast led to a 1.9-fold increase in 2-phenylethanol levels, whereas the decreases in alkanes, acids and aldehydes levels were attributed to the hydrophobic substrate metabolizing pathways that were unique to Y. lipolytica. Hence, this work showed that Y. lipolytica fermentation of green coffee beans resulted in the modification of the aroma precursors and volatile composition of green coffees.

Modulation of the volatile and non-volatile profiles of coffee fermented with Yarrowia lipolytica: II. Roasted coffee

Co-reporter:Liang Wei Lee, Geng Yu Tay, Mun Wai Cheong, Philip Curran, Bin Yu, Shao Quan Liu

LWT - Food Science and Technology 2017 Volume 80(Volume 80) pp:

Publication Date(Web):1 July 2017

DOI:10.1016/j.lwt.2017.01.070

•Volatile profiles of roasted coffee were modulated by Y. lipolytica fermentation.•Effects of Y. lipolytica fermentation were most prominent at light roast level.•Certain fermentation effects observed in green coffee were preserved after roasting.•Total volatile phenol levels in light roasted coffee increased after fermentation.•Y. lipolytica fermentation of green coffee bean can promote coffee aroma modulation.The fermentation of green coffee beans by Yarrowia lipolytica led to significant changes in the volatile and non-volatile profiles of green coffees (Part I). Therefore, the objective of this continuation study was to evaluate the effects of fermentation after roasting by characterizing the volatile profiles of coffees at three different roast levels and non-volatile profiles of coffee where the effects of fermentation on volatiles were most prominent (light roast). Y. lipolytica fermentation led to significant changes in the volatile profiles of roasted coffees which arose from both the modification of aroma precursors and the retention of volatile profile changes observed in green fermented coffees. The levels of 4-vinylguaiacol and 4-vinylphenol were 1.2-fold and 1.6-fold higher in light roasted fermented coffees respectively and could be explained by the higher levels detected in green fermented coffees before roasting. The levels of γ-butyrolactone were 5 times higher in light roasted fermented coffees than unfermented coffees. The increase in sulfur compounds levels and decrease in ketones levels were attributed to changes in the concentrations of aroma precursors like sugars and amino acids. Thus, this study highlighted the potential of utilizing yeast fermentation of green coffee beans for coffee aroma modulation.

Physico-chemical parameters and proanthocyanidin profiles of cranberries cultivated in New Zealand

Co-reporter:Yuyun Lu, Bernadette Natalia Pekerti, Zhi Siang Toh, Fraser Broom, Geoffrey Savage, Shao Quan Liu, Dejian Huang

Journal of Food Composition and Analysis 2017 Volume 63(Volume 63) pp:

Publication Date(Web):1 October 2017

DOI:10.1016/j.jfca.2017.07.002

•Different cultivars of cranberries contain a wide range of organic acid contents.•Proanthocyanidins profiles were similar among the different cultivars investigated.•A-type (epi)catechin units were the main constituents of the proanthocyanidins.•Crowley and Howes showed promise as potential food resources for health use.Twenty-one cultivars of cranberry fruits (Vaccinium macrocarpon) grown in New Zealand were analysed for their physico-chemical characteristics including average fruit weight, total soluble solids content, pH, total titratable acidity, organic acids, and total anthocyanins. In addition, the total proanthocyanidin contents of the fruit were determined using 4-dimethylaminocinnamaldehyde assay, and the profiles were characterised using matrix-assisted laser desorption/ionization time of flight mass spectra. Between the different cultivars, there was a range of average fruit weight (0.75–1.84 g), total soluble solids content (9.7–12.8%), juice pH (2.61–2.86), total titratable acidity (3.74–8.77 g citric acid/L juice) and total anthocyanin content (1.63–2.87 mg cyanidin-3-glucoside/g dry weight). The 21 cranberry cultivars exhibited similar high performance liquid chromatography profiles for proanthocyanidins using a diol column. The cultivars of Crowley and Howes with the higher contents were found to contain mainly A type (epi)catechin extending units. Therefore, Crowley and Howes with high proanthocyanidin contents would be the best choice of the cultivars studied for the promotion of urinary tract health.

Biotransformation of soy whey into soy alcoholic beverage by four commercial strains of Saccharomyces cerevisiae

Co-reporter:Jian-Yong Chua, Yuyun Lu, Shao-Quan Liu

International Journal of Food Microbiology 2017 Volume 262(Volume 262) pp:

Publication Date(Web):4 December 2017

DOI:10.1016/j.ijfoodmicro.2017.09.007

•Zero-waste approach to soy whey disposal issue.•Soy whey biotransformed to soy alcoholic beverage with minimal supplementation using wine yeasts.•Isoflavones glucosides were hydrolyzed to isoflavones aglycones.•Indigenous aroma compounds replaced with new esters and higher alcohols.Soy whey is a liquid waste stream generated from tofu and soy protein manufacturing, and is commonly disposed of into the drainage system in food industry. Instead of disposing of soy whey as a waste, it could be used to produce alcoholic beverages. This study investigated the feasibility of converting soy whey into soy alcoholic beverage using four commercial Saccharomyces cerevisiae strains as a zero-waste approach to tackle the soy whey disposal issue. The four Saccharomyces yeasts grew by approximately 2 log CFU/mL and produced approximately 7–8% (v/v) of ethanol. Isoflavone glucosides were hydrolyzed and transformed into isoflavone aglycones, increasing the antioxidant capacity. New aroma-active volatiles, especially esters and higher alcohols, were produced and imparted fruity and floral notes to the soy alcoholic beverage. Therefore, alcoholic fermentation would serve as a solution toward zero-waste manufacturing by biotransforming soy whey into a world's first novel functional alcoholic beverage naturally enriched with free isoflavones.

Modulation of coffee aroma via the fermentation of green coffee beans with Rhizopus oligosporus: II. Effects of different roast levels

Co-reporter:Liang Wei Lee, Mun Wai Cheong, Philip Curran, Bin Yu, Shao Quan Liu

Food Chemistry 2016 Volume 211() pp:925-936

Publication Date(Web):15 November 2016

DOI:10.1016/j.foodchem.2016.05.073

•The effects of R. oligosporus fermentation were evaluated over three roast levels.•Total pyrazines levels in roasted coffees increased after fermentation.•The sweet attribute of light and dark roasted coffees increased after fermentation.•Fermentation effects were most distinctive at light roast level.•R. oligosporus fermentation of green coffee beans led to modulation of coffee aroma.This study aims to evaluate how changes of the volatile and non-volatile profiles of green coffees induced by Rhizopus oligosporus fermentation of green coffee beans (Part I) translated to changes in the volatile and aroma profiles of light, medium and dark roasted coffees and non-volatile profile of roasted coffee where fermentation effects were most distinctive (light roast). R. oligosporus fermentation resulted in 1.7-, 1.5- and 1.3-fold increases in pyrazine, 2-methylpyrazine and 2-ethylpyrazine levels in coffees of all roast degrees, respectively. This corresponded with the greater extent of amino acids degradation in light roasted fermented coffee. Ethyl palmitate was detected exclusively in medium and dark roasted fermented coffees. The sweet attribute of light and dark roasted coffees were increased following fermentation along with other aroma profile changes that were roast degree specific. This work aims to develop a direct but novel methodology for coffee aroma modulation through green coffee beans fermentation.

Modulation of coffee aroma via the fermentation of green coffee beans with Rhizopus oligosporus: I. Green coffee

Co-reporter:Liang Wei Lee, Mun Wai Cheong, Philip Curran, Bin Yu, Shao Quan Liu

Food Chemistry 2016 Volume 211() pp:916-924

Publication Date(Web):15 November 2016

DOI:10.1016/j.foodchem.2016.05.076

•Green coffee beans were fermented with a food-grade fungus Rhizopus oligosporus.•Volatile and non-volatile profiles of green coffee after fermentation were examined.•Ferulic and caffeic acids degradation elevated the levels of total volatile phenols.•Proteolysis during fermentation led to increase in the amino acids concentrations.•R. oligosporus fermentation induced changes to the aroma precursors in green coffee.Modulation of coffee aroma via the biotransformation/fermentation of different coffee matrices during post-harvest remains sparingly explored despite some studies showing their positive impacts on coffee aroma. Therefore, this is an unprecedented study aimed at modulating coffee aroma via the fermentation of green coffee beans with a food-grade fungus Rhizopus oligosporus. The objective of part I of this two-part study was to characterize the volatile and non-volatile profiles of green coffee beans after fermentation. Proteolysis during fermentation resulted in 1.5-fold increase in the concentrations of proline and aspartic acid which exhibited high Maillard reactivity. Extensive degradation of ferulic and caffeic acids led to 2-fold increase in the total concentrations of volatile phenolic derivatives. 36% of the total volatiles detected in fermented green coffee beans were generated during fermentation. Hence, the work presented demonstrated that R. oligosporus fermentation of green coffee beans could induce modification of the aroma precursors of green coffees.

Coffee fermentation and flavor – An intricate and delicate relationship

Co-reporter:Liang Wei Lee, Mun Wai Cheong, Philip Curran, Bin Yu, Shao Quan Liu

Food Chemistry 2015 Volume 185() pp:182-191

Publication Date(Web):15 October 2015

DOI:10.1016/j.foodchem.2015.03.124

•Coffee fermentation and aroma formation share an intricate and delicate relation.•Coffee aroma is easily impacted by fermentation process during coffee processing.•Controlled fermentation during coffee processing imparts desirable attributes.•Fermentation has been applied as unconventional avenue for coffee aroma modulation.•Green coffee bean fermentation could promote modulation of coffee aroma.The relationship between coffee fermentation and coffee aroma is intricate and delicate at which the coffee aroma profile is easily impacted by the fermentation process during coffee processing. However, as the fermentation process in coffee processing is conducted mainly for mucilage removal, its impacts on coffee aroma profile are usually neglected. Therefore, this review serves to summarize the available literature on the impacts of fermentation in coffee processing on coffee aroma as well as other unconventional avenues where fermentation is employed for coffee aroma modulation. Studies have noted that proper control over the fermentation process imparts desirable attributes and prevents undesirable fermentation which generates off-flavors. Other unconventional avenues in which fermentation is employed for aroma modulation include digestive bioprocessing and the fermentation of coffee extracts and green coffee beans. The latter is an area that should be explored further with appropriate microorganisms given its potential for coffee aroma modulation.

Ester Synthesis in Aqueous Media by Lipase: Alcoholysis, Esterification and Substrate Hydrophobicity

Co-reporter:Jingcan Sun;Shao-Quan Liu

Journal of Food Biochemistry 2015 Volume 39( Issue 1) pp:11-18

Publication Date(Web):

DOI:10.1111/jfbc.12104

Abstract

Lipases are versatile biocatalysts commonly used for flavor ester synthesis in media with low-water activity. This research studied the mechanism of ester synthesis by lipase Palatase in coconut cream and phosphate buffer with alcohols and fatty acids. When ethanol was added as the alcohol substrate, hydrolysis of triglycerides dominated over synthesis of esters. When fusel alcohols (fusel oil) were used as the alcohol substrate, ester synthesis dominated over lipid hydrolysis. However, there was no visible pattern of fatty acid production and then reutilization in relation to ester synthesis in either case. Higher consumption of octanoic acid was obtained than that of butyric acid in both coconut cream and buffer systems spiked with the same alcohol. This indicated the preferential utilization of more hydrophobic substrates for esterification by lipase in aqueous media. These results suggest that the lipase Palatase-catalyzed ester synthesis in aqueous media was mainly hydrophobicity-dependent esterification.

Practical Applications

Esters are important flavor compounds that are applied in food products. The effects of substrate hydrophobicity and reaction environment on the catalytic behavior of a lipase during ester synthesis in an aqueous system of coconut cream and fusel oil were investigated. Useful information was obtained on the in situ generation of esters in food materials. This study has implications for lipase-catalyzed synthesis of flavor esters in other aqueous food matrices.

Optimization of methionol bioproduction by Saccharomyces cerevisiae using response surface methodology

Co-reporter:Heng-Qian Lwa;Jingcan Sun;Shao-Quan Liu

Annals of Microbiology 2015 Volume 65( Issue 1) pp:197-205

Publication Date(Web):2015 March

DOI:10.1007/s13213-014-0850-y

Methionol (3-methylthio-1-propanol) is an important volatile sulphur-containing alcohol that may significantly impact food flavour. The purpose of this research is to investigate the bioproduction of methionol from L-methionine catabolism by Saccharomyces cerevisiae EC-1118. The biotransformation was carried out in coconut cream supplemented with L-methionine. Response surface methodology was applied for the optimization of fermentation conditions to achieve a high yield of methionol. A second-order polynomial model (R2 = 0.912) was established based on the experimental data obtained in this study using multiple regression analysis. To obtain more accurate prediction results, a reduced quadratic model was obtained through backward elimination. Based on the reduced model, the optimal conditions for maximum methionol production were determined to be 0.30 % (w/v) of L-methionine, 0.10 % (w/v) of yeast extract and zero level of diammonium phosphate. Under these optimal conditions, a methionol concentration of 240.7 ± 17.4 μg/mL was achieved. This experimental result was in close agreement with the predicted value of 243.5 μg/mL, indicating that this model was adequate. These results indicate that fermentation by S. cerevisiae in L-methionine-supplemented coconut cream medium is an effective method for the production of methionol. Large-scale fermentation trials are needed to provide valuable information for industrial production.

Saccharomyces cerevisiae EC-1118 enhances the survivability of probiotic Lactobacillus rhamnosus HN001 in an acidic environment

Co-reporter:Phebe Lixuan Lim;Mingzhan Toh

Applied Microbiology and Biotechnology 2015 Volume 99( Issue 16) pp:6803-6811

Publication Date(Web):2015 August

DOI:10.1007/s00253-015-6560-y

The present study attempted to partially characterize and elucidate the viability-enhancing effect of a yeast strain Saccharomyces cerevisiae EC-1118 on a probiotic strain Lactobacillus rhamnosus HN001 under acidic conditions using a model system (non-growing cells). The yeast was found to significantly enhance (P < 0.05) the viability of the probiotic strain under acidic conditions (pH 2.5 to 4.0) by 2 to 4 log cycles, and the viability-enhancing effects were observed to be influenced by pH, and probiotic and yeast concentrations. Microscopic observation and co-aggregation assay revealed that the viability-enhancing effect of the yeast could be attributed to direct cell-cell contact co-aggregation mediated by yeast cell surface and/or cell wall components or metabolites. Furthermore, non-viable yeast cells killed by thermal means were observed to enhance the viability of the probiotic strain as well, suggesting that the surface and/or cell wall component(s) of the yeast contributing to co-aggregation was heat-stable. Cell-free yeast supernatant was also found to enhance the viability of the probiotic strain, indicating the presence of protective yeast metabolite(s) in the supernatant. These findings laid the foundation for further understanding of the mechanism(s) involved and for developing novel microbial starter cultures possibly without the use of live yeast for ambient-stable high-moisture probiotic foods.

Chemical and enzymatic synthesis of a library of 2-phenethyl esters and their sensory attributes

Co-reporter:Cheng Li, Jingcan Sun, Tianhu Li, Shao-Quan Liu, Dejian Huang

Food Chemistry 2014 Volume 154() pp:205-210

Publication Date(Web):1 July 2014

DOI:10.1016/j.foodchem.2013.12.102

•Enzymatic method is suitable for synthesising 2-phenethyl esters.•Fatty acid chain length determines the flavour attributes of 2-phenethyl esters.•Butter oil is a cost-effective material for 2-phenethyl ester flavourings.We report a simple enzymatic approach to synthesise phenethyl esters as natural flavouring materials. Chemical and lipase-catalysed esterification reactions between fatty acids of C4–C18 and 2-phenethyl alcohol were studied. Both methods were compared qualitatively and quantitatively by GC–MS/FID. The acid and thermal stabilities of 2-phenethyl esters were excellent and can meet the requirements of food matrices under most processing conditions. Sensory evaluation showed that each 2-phenethyl ester with a different carbon-chain-length fatty acid had unique sensory notes. Moreover, through Lipozyme TL IM-mediated transesterification, valuable 2-phenethyl alcohol-derived esters were synthesised from butter oil and 2-phenethyl alcohol. The influence of several physicochemical parameters (temperature, substrate molar ratio, enzyme loading, shaking speed and time) on the transesterification reaction was investigated to give optimal reaction conditions, leading to a high yield of 80.0%.

Biosynthesis of flavor esters in coconut cream through coupling fermentation and lipase-catalyzed biocatalysis

Co-reporter:Jingcan Sun;Yunwei Lim;Shao-Quan Liu

European Journal of Lipid Science and Technology 2013 Volume 115( Issue 10) pp:1107-1114

Publication Date(Web):

DOI:10.1002/ejlt.201300144

The aim of this research was to study the biosynthesis of natural flavor-active ethyl esters with a commercial lipase, Palatase 20 000 L, in coconut cream by coupling with yeast alcoholic fermentation. Alcoholic fermentation was carried out by Saccharomyces cerevisiae, which generated ethanol as one substrate for ester synthesis. Lipase was added into the fermentation medium at three different time points (12, 24, and 48 h) during the time-course fermentation of 72 h. The concentrations of ethyl octanoate, ethyl decanoate, and ethyl laurate were the highest when lipase was added at 12 h, indicating early coupling of ethanol production with ester synthesis catalyzed by lipase. Although the growth of S. cerevisiae was slightly inhibited when lipase was added into the fermentation medium due to the formation of fatty acids, no adverse effect on ester synthesis was observed. This novel approach may be useful in the production of relevant flavors of fermented coconut cream with lipase treatment, which could be used as a new food ingredient.

Practical applications: Esters are a group of valuable flavor compounds that have wide applications in a variety of food products. In this work, we proposed one effective approach of coupling yeast alcoholic fermentation and lipase-catalyzed biocatalysis to synthesize natural fatty acid ethyl esters in coconut cream. This method provides a novel application of coconut cream for ester synthesis. In addition, the esters formed can be considered as natural according to current regulations. The ethanol generated can be effectively utilized for ester synthesis, therefore, complying with the Halal rules. The end product can be possibly used as a natural flavoring in the food industry after sensory evaluation and proper process. The esters formed may be further separated and purified as pure flavor compounds.

Determination of Flavor Esters in Enzymatically Transformed Coconut Oil

Co-reporter:Jingcan Sun;Jin Hua Chin;Bin Yu;Philip Curran;Shao-Quan Liu

Journal of Food Biochemistry 2013 Volume 37( Issue 6) pp:654-660

Publication Date(Web):

DOI:10.1111/j.1745-4514.2012.00660.x

ABSTRACT

The lipase-catalyzed transesterification of coconut oil with fusel oil was investigated in this study. Various aroma-active octanoic acid esters, such as ethyl-, butyl-, propyl-, isobutyl- and (iso)amyl octanoate, were synthesized in addition to other esters. To determine the amount of flavor esters, a simple yet effective sample preparation method through refrigeration was developed to separate valuable fatty acid esters from monoglycerides, diglycerides and triglycerides. With this sample preparation method, gas chromatography coupled with mass spectrometry and flame ionization detector was applied to determine flavor esters in transesterified coconut oil with a total run time of 51 min. The levels of coefficient of variation were within 2% and the recovery rates were in the range of 89.5–100.0%, indicating good accuracy and high precision. The sample preparation and quantification method established appears to be useful for the determination of a wide range of fatty acid esters in oil samples.

PRACTICAL APPLICATIONS

Fatty acid esters, especially short-chain fatty acid esters, are important flavoring agents applied in the food industry. Using lipase as the biocatalyst to synthesize desirable flavor fatty acid esters from lipids and alcohols is gaining the interest of researchers, since the esters formed by this method are deemed as natural. The reaction equilibrium was achieved at around 20 h. For industrial production of flavor fatty acid esters, it is essential to monitor the amount of these target compounds in the reaction solutions. In this study we developed a simple and effective quantification method to determine the esters in transesterified coconut oil which may also be applicable for the analysis of esters in other oil samples such as lipid-derived biofuels.

Optimisation of flavour ester biosynthesis in an aqueous system of coconut cream and fusel oil catalysed by lipase

Co-reporter:Jingcan Sun, Bin Yu, Philip Curran, Shao-Quan Liu

Food Chemistry 2012 Volume 135(Issue 4) pp:2714-2720

Publication Date(Web):15 December 2012

DOI:10.1016/j.foodchem.2012.06.119

Coconut cream and fusel oil, two low-cost natural substances, were used as starting materials for the biosynthesis of flavour-active octanoic acid esters (ethyl-, butyl-, isobutyl- and (iso)amyl octanoate) using lipase Palatase as the biocatalyst. The Taguchi design method was used for the first time to optimize the biosynthesis of esters by a lipase in an aqueous system of coconut cream and fusel oil. Temperature, time and enzyme amount were found to be statistically significant factors and the optimal conditions were determined to be as follows: temperature 30 °C, fusel oil concentration 9% (v/w), reaction time 24 h, pH 6.2 and enzyme amount 0.26 g. Under the optimised conditions, a yield of 14.25 mg/g (based on cream weight) and signal-to-noise (S/N) ratio of 23.07 dB were obtained. The results indicate that the Taguchi design method was an efficient and systematic approach to the optimisation of lipase-catalysed biological processes.Highlights► Coconut cream and fusel oil, the low-cost natural materials, were converted to valuable esters. ► The lipase Palatase ® 20000L was used as the biocatalyst. ► The biocatalysis process was carried out in an aqueous system. ► The reaction conditions were optimized using the Taguchi method to obtain high yield of esters.

Lipase-catalysed transesterification of coconut oil with fusel alcohols in a solvent-free system

Co-reporter:Jingcan Sun, Bin Yu, Philip Curran, Shao-Quan Liu

Food Chemistry 2012 Volume 134(Issue 1) pp:89-94

Publication Date(Web):1 September 2012

DOI:10.1016/j.foodchem.2012.02.070

The conversion of coconut oil and fusel alcohols, the sustainable and low-cost natural materials, to valuable products through Lipozyme TL IM-catalysed transesterification was investigated in a solvent-free system. Flavour esters, especially the octanoic acid esters (ethyl-, butyl-, isobutyl-, propyl- and (iso)amyl octanoate), were formed during the transesterification reactions. The reaction parameters were optimised as follows: molar ratio of 3.0:1 (alcohol to oil), enzyme loading of 15% wt/wt, reaction temperature of 23 °C, shaking speed of 130 rpm, and reaction time of 20 h. Further, the operational stability of Lipozyme TL IM was improved through washing with solvents, after which the enzyme could be continuously used for at least 100 h within 5 batches’ reactions without significant loss of activity. The results indicate that coconut oil and fusel alcohols can be effectively converted to valuable flavour esters through the Lipozyme TL IM-catalysed transesterification.Highlights► Coconut oil and fusel alcohols were converted to flavour esters by lipase. ► The biocatalysis process was carried out in a solvent-free system. ► Transesterification was optimised to obtain high yield of esters. ► Enzyme operational stability was improved by solvent-wash treatment.

Volatile sulphur compounds and pathways of l-methionine catabolism in Williopsis yeasts

Co-reporter:Amelia W. J. Tan;Pin-Rou Lee;Yi-Xin Seow

Applied Microbiology and Biotechnology 2012 Volume 95( Issue 4) pp:1011-1020

Publication Date(Web):2012 August

DOI:10.1007/s00253-012-3963-x

Volatile sulphur compounds (VSCs) are important to the food industry due to their high potency and presence in many foods. This study assessed for the first time VSC production and pathways of l-methionine catabolism in yeasts from the genus Williopsis with a view to understanding VSC formation and their potential flavour impact. Five strains of Williopsis saturnus (var. saturnus, var. subsufficiens, var. suavolens, var. sargentensis and var. mrakii) were screened for VSC production in a synthetic medium supplemented with l-methionine. A diverse range of VSCs were produced including dimethyl disulphide, dimethyl trisulphide, 3-(methylthio)-1-propanal (methional), 3-(methylthio)-1-propanol (methionol), 3-(methylthio)-1-propene, 3-(methylthio)-1-propyl acetate, 3-(methylthio)-1-propanoic acid (methionic acid) and ethyl 3-(methylthio)-1-propanoate, though the production of these VSCs varied between yeast strains. W. saturnus var. saturnus NCYC22 was selected for further studies due to its relatively high VSC production. VSC production was characterised step-wise with yeast strain NCYC22 in coconut cream at different l-methionine concentrations (0.00–0.20%) and under various inorganic sulphate (0.00–0.20%) and nitrogen (ammonia) supplementation (0.00–0.20%), respectively. Optimal VSC production was obtained with 0.1% of l-methionine, while supplementation of sulphate had no significant effect. Nitrogen supplementation showed a dramatic inhibitory effect on VSC production. Based on the production of VSCs, the study suggests that the Ehrlich pathway of l-methionine catabolism is operative in W. saturnus yeasts and can be manipulated by adjusting certain nutrient parameters to control VSC production.

Lipase-catalysed synthesis of natural aroma-active 2-phenylethyl esters in coconut cream

Co-reporter:Hui Shan Grace Tan, Bin Yu, Philip Curran, Shao Quan Liu

Food Chemistry 2011 Volume 124(Issue 1) pp:80-84

Publication Date(Web):1 January 2011

DOI:10.1016/j.foodchem.2010.05.108

The aim of this research was to study the feasibility of biosynthesising natural aroma-active 2-phenylethyl esters in coconut cream via biocatalysis. Five commercial fungal lipases (Palatase 20 000L, Lipase AYS “Amano”, Lipase A “Amano” 12, Piccantase A and Piccantase AN) were screened for their ability to produce 2-phenylethyl hexanoate and 2-phenylethyl octanoate from coconut cream supplemented with natural 2-phenylethanol. Palatase 20 000L and Lipase AYS “Amano” showed the greatest potential for the synthesis of 2-phenylethyl esters. The biosynthetic reaction by the lipase Palatase 20 000L was further studied under different temperature, pH, enzyme and substrate concentrations, with maximum ester synthesis obtained at 9% v/v 2-phenylethanol and 2.15–8.60 mg enzyme protein/100 ml of reaction mixture. A temperature range of 30–53 °C and a pH range of 5.2–8.5 had little effect on the lipase Palatase activity, respectively. The ester-synthesising reaction appeared to proceed by both alcoholysis and esterification.

Quantitative analysis of volatiles in transesterified coconut oil by headspace-solid-phase microextraction-gas chromatography–mass spectrometry

Co-reporter:Jingcan Sun, Bin Yu, Philip Curran, Shao-Quan Liu

Food Chemistry 2011 Volume 129(Issue 4) pp:1882-1888

Publication Date(Web):15 December 2011

DOI:10.1016/j.foodchem.2011.05.138

A simple and fast headspace-solid-phase microextraction (HS-SPME) method coupled with gas chromatography–mass spectrometry (GC–MS) was developed for the analysis of volatile compounds in transesterified coconut oil by applying solvent dilution. Solvent dilution conditions (solvent type and solvent amount) and HS-SPME sampling parameters (adsorption temperature and time) were optimised through monitoring the adsorption result of the selected volatiles (octanoic acid esters) in transesterified coconut oil samples. The incubation of methanol (800 μl)-diluted oil (200 μl) sample at 60 °C for 30 min led to the best result. The method was further validated by determining the calibration linear range, correlation coefficient (R2), accuracy, precision, limit of detection and limit of quantification through spiking standards into the blank matrix consisting of coconut oil and methanol. This method may also be applicable for detection and determination of volatile compounds in other transesterified oil samples.Highlights► Coconut oil and fusel alcohols are transesterified by immobilised lipase. ► Modification of oil matrix with methanol minimises SPME fibre overloading. ► Optimisation of time and temperature enables efficient SPME extraction. ► Quantification of esters is achieved by HS-SPME-GC–MS-FID.

Profile of volatile compounds during papaya juice fermentation by a mixed culture of Saccharomyces cerevisiae and Williopsis saturnus

Co-reporter:P.-R. Lee, Y.-L. Ong, B. Yu, P. Curran, S.-Q. Liu

Food Microbiology (October 2010) Volume 27(Issue 7) pp:853-861

Publication Date(Web):1 October 2010

DOI:10.1016/j.fm.2010.05.010

This study investigated the formation and utilization of volatile compounds during papaya juice fermentation by a mixed culture of Saccharomyces cerevisiae and Williopsis saturnus. Time-course papaya juice fermentations were carried out using pure cultures of S. cerevisiae var. bayanus R2 and W. saturnus var. mrakii NCYC2251 and a mixed culture of the two yeasts at a ratio of 1:1000 (R2:NCYC2251). Changes in S. cerevisiae cell population, Brix, sugar consumption and pH were similar in the mixed culture and in the S. cerevisiae monoculture. There was an early growth arrest of W. saturnus in the mixed culture fermentation. A range of volatile compounds were produced during fermentation including fatty acids, alcohols, aldehydes and esters and some volatile compounds including those initially present in the juice were utilized. The mixed culture fermentation of S. cerevisiae and W. saturnus benefited from the presence of both yeasts, with more esters being produced than the S. cerevisiae monoculture and more alcohols being formed than the W. saturnus monoculture. The study suggests that papaya juice fermentation with a mixed culture of S. cerevisiae and W. saturnus may be able to result in the formation of more complex aroma compounds and higher ethanol level than those using single yeasts.

Evaluation of the performance of Torulaspora delbrueckii, Williopsis saturnus, and Kluyveromyces lactis in lychee wine fermentation

Co-reporter:Dai Chen, Zhi Yin Yap, Shao-Quan Liu

International Journal of Food Microbiology (3 August 2015) Volume 206() pp:45-50

Publication Date(Web):3 August 2015

DOI:10.1016/j.ijfoodmicro.2015.04.020

•These three non-Saccharomyces yeast scould partially retain terpenes and terpenoids.•T. delbrueckii had the highest fermentative capacity and the highest production of ethanol, higher alcohols and ethyl esters.•W. saturnus produced the highest levels of acetate esters, but ethanol was lowest.•K. lactis had the greatest ability to retain geraniol and citronellol.•T. delbrueckii PRELUDE was a promising strain for lychee wine fermentation.This study evaluated the effects of three non-Saccharomyces yeasts, namely Torulaspora delbrueckii PRELUDE, Williopsis saturnus NCYC22, and Kluyveromyces lactis KL71 on lychee juice fermentation. The fermentation performance of these non-Saccharomyces yeasts was significantly different. T. delbrueckii PRELUDE had the fastest rate of growth and high sugar consumption. W. saturnus NCYC22 used the lowest amount of sugars, but consumed the highest amount of nitrogen. Correspondingly, strain PRELUDE produced the highest level of ethanol (7.6% v/v), followed by strain KL71 (3.4% v/v) and strain NCYC22 (0.8% v/v). Aroma character-impact terpenes and terpenoids could be partially retained in all lychee wines, with higher odour activity values (OAVs) of geraniol and citronellol in strain KL71. However, strain KL71 and strain NCYC22 over-produced ethyl acetate. Strain PRELUDE had a better ability to generate high levels of ethanol, isoamyl alcohol, 2-phenylethyl alcohol, ethyl octanoate, and ethyl decanoate and retained high OAVs of lychee aroma-character compounds cis-rose oxide (16.5) and linalool (3.5). Thus, it is deemed to be a promising non-Saccharomyces yeast for lychee wine fermentation.

Induction of simultaneous and sequential malolactic fermentation in durian wine

Co-reporter:Fransisca Taniasuri, Pin-Rou Lee, Shao-Quan Liu

International Journal of Food Microbiology (2 August 2016) Volume 230() pp:1-9

Publication Date(Web):2 August 2016

DOI:10.1016/j.ijfoodmicro.2016.04.006

•Simultaneous and sequential malolactic fermentations were induced in durian wine.•Malolactic fermentations (MLFs) resulted in low amounts of acetic acid in durian wine.•Simultaneous MLF produced higher concentrations of terpenes and acetate esters.•Sequential MLF increased levels of medium- and long-chain ethyl esters.•MLF is an effective way of modulating volatile profile of durian wine.This study represented for the first time the impact of malolactic fermentation (MLF) induced by Oenococcus oeni and its inoculation strategies (simultaneous vs. sequential) on the fermentation performance as well as aroma compound profile of durian wine. There was no negative impact of simultaneous inoculation of O. oeni and Saccharomyces cerevisiae on the growth and fermentation kinetics of S. cerevisiae as compared to sequential fermentation. Simultaneous MLF did not lead to an excessive increase in volatile acidity as compared to sequential MLF. The kinetic changes of organic acids (i.e. malic, lactic, succinic, acetic and α-ketoglutaric acids) varied with simultaneous and sequential MLF relative to yeast alone. MLF, regardless of inoculation mode, resulted in higher production of fermentation-derived volatiles as compared to control (alcoholic fermentation only), including esters, volatile fatty acids, and terpenes, except for higher alcohols. Most indigenous volatile sulphur compounds in durian were decreased to trace levels with little differences among the control, simultaneous and sequential MLF. Among the different wines, the wine with simultaneous MLF had higher concentrations of terpenes and acetate esters while sequential MLF had increased concentrations of medium- and long-chain ethyl esters. Relative to alcoholic fermentation only, both simultaneous and sequential MLF reduced acetaldehyde substantially with sequential MLF being more effective. These findings illustrate that MLF is an effective and novel way of modulating the volatile and aroma compound profile of durian wine.

Impact of addition of aromatic amino acids on non-volatile and volatile compounds in lychee wine fermented with Saccharomyces cerevisiae MERIT.ferm

Co-reporter:Dai Chen, Jing Yee Chia, Shao-Quan Liu

International Journal of Food Microbiology (17 January 2014) Volume 170() pp:12-20

Publication Date(Web):17 January 2014

DOI:10.1016/j.ijfoodmicro.2013.10.025

•Single aromatic amino acid had no impact on lychee wine fermentation dynamics.•Single aromatic amino acid reduced proline consumption and decreased glycerol formed.•l-Phenylalanine addition increased 2-phenylethyl alcohol, and its esters.The impact of individual aromatic amino acid addition (l-phenylalanine, l-tryptophan and l-tyrosine) on non-volatile and volatile constituents in lychee wine fermented with Saccharomyces cerevisiae var. cerevisiae MERIT.ferm was studied. None of the added amino acids had any significant effect on the yeast cell count, pH, soluble solid contents, sugars and ethanol. The addition of l-phenylalanine significantly reduced the production of pyruvic and succinic acids. The addition of each amino acid dramatically reduced the consumption of proline and decreased the production of glycerol. Supplementation of the lychee juice with l-phenylalanine resulted in the formation of significantly higher amounts of 2-phenylethyl alcohol, 2-phenylethyl acetate, 2-phenylethyl isobutyrate and 2-phenylethyl hexanoate. In contrast, supplementation with l-tryptophan and l-tyrosine had negligible effects on the volatile profile of lychee wines. These findings suggest that selectively adding amino acids may be used as a tool to modulate the volatile profile of lychee wines so as to diversify and/or intensify wine flavour and style.