Effect of starch addition on the physicochemical properties, molecular interactions, structures, and in vitro digestibility of the plant-based egg analogues.

This study investigated the gelling mechanisms of plant-based eggs modified with corn starch (CS), glutinous rice starch (GS), or potato starch (PS) at soy protein isolate (SPI)/starch ratios of 10:4, 8:6, and 6:8 (w/w). A plant-based omelet with SPI/PS 8:6 matched the texture (especially cohesiveness (0.75 vs 0.79)) and specific volume (1.28 vs 1.32 cm3/g) of an egg omelet best. This was attributed to greater protein-starch interactions (H-bonding, ionic bonding) that supported its strong structure. SPI/CS 8:6, SPI/GS 8:6, SPI/PS 10:4, and SPI/PS 6:8 demonstrated more ruptured granules and formed weaker gels. These proposed models were verified by nuclear magnetic resonance (NMR)-based metabolomics, where the stronger SPI/PS 8:6 gel released less metabolites after in vitro digestion. Through understanding different roles of starch in plant-based egg systems, this study suggests more potential applications of starch in modifying food properties.

Biotransformation of pork trimmings into protein hydrolysate using microbial proteases aided by response surface methodology.

Meat processing generates significant amounts of by-products such as trimmings that require further valorization. In this study, pork trimmings were transformed with proteases to protein hydrolysates that may find applications as nutritional and/or flavouring ingredients. Four microbial proteases-Flavourzyme, Protamex, Alcalase, and Neutrase were explored to hydrolyze pork trimmings. Flavourzyme, which showed the highest degree of hydrolysis (DH), was selected to optimize the key hydrolytic parameters using response surface methodology (RSM) with Box-Behnken design. The optimal conditions were found to be 6: 100 (enzyme/substrate ratio), 50 °C, and pH 6 for a maximum DH at 48% after 6 h of hydrolysis. The protein hydrolysate was high in free amino acids (17 g/100 g dry weight), of which essential and taste-active amino acids accounted for 42% and 20%, respectively. The obtained hydrolysate may be considered suitable as a nutritional and/or flavouring ingredient.

The Possible Reduction Mechanism of Volatile Sulfur Compounds during Durian Wine Fermentation Verified in Modified Buffers.

Durian fruit is rich in volatile sulfur compounds (VSCs), especially thiols and disulfides, which contribute to its onion-like odor. After fermentation, these VSCs were reduced to trace or undetectable levels in durian wine. The possible reduction mechanism of these VSCs (especially diethyl disulfide and ethanethiol) was investigated in a modified buffer in the presence of sulfite at different pH. An interconversion between diethyl disulfide and ethanethiol was found to be dependent on the pH: the higher the pH, the higher production of ethanethiol. It is suggested that, during durian wine fermentation, disulfides endogenous to durian pulp might be firstly converted into their corresponding thiols in the presence of reductant sulfite formed by yeast. The produced thiols as well as the thiols endogenous to the durian pulp were then removed by the mannoproteins of yeast lees.

The effects of co- and sequential inoculation of Torulaspora delbrueckii and Pichia kluyveri on chemical compositions of durian wine.

This is a first study on using two non-Saccharomyces yeasts, Torulaspora delbrueckii Biodiva and Pichia kluyveri FrootZen to produce durian wine via co-inoculation (Co-I) and sequential inoculation (Seq-I). T. delbrueckii inhibited the growth of P. kluyveri and P. kluyveri also partly retarded the growth of T. delbrueckii in Co-I and Seq-I treatments. Co-I and Seq-I produced similar levels of ethanol to T. delbrueckii Biodiva monoculture. In addition, Seq-I increased malic acid degradation and higher succinic acid production. Compared with T. delbrueckii Biodiva, Co-I produced similar amounts of ethyl esters, higher alcohols and moderately increased levels of ethyl acetate. Seq-I 2th (T. delbrueckii inoculated after 2 days fermentation with P. kluyveri) and Seq-I 5th produced excessive amounts of ethyl acetate (≥ 80 mg/L) but relatively lower levels of higher alcohols. This study suggested that Co-I could complete alcoholic fermentation with more complex aromas and might be novel way for wine making.

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

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.

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

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 (>80mg/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.

Biotransformation of chemical constituents of durian wine with simultaneous alcoholic fermentation by Torulaspora delbrueckii and malolactic fermentation by Oenococcus oeni.

This work represents the first study on the biotransformation of chemical constituents of durian wine via simultaneous alcoholic fermentation (AF) and malolactic fermentation (MLF) with non-Saccharomyces yeast and lactic acid bacteria (LAB), namely, Torulaspora delbrueckii Biodiva and Oenococcus oeni PN4. The presence of PN4 improved the utilization of sugars but did not affect ethanol production. MLF resulted in the significant degradation of malic acid with corresponding increases in pH and lactic acid. The final concentrations of acetic acid (1.29 g/L) and succinic acid (3.70 g/L) in simultaneous AF and MLF were significantly higher than that in AF (1.05 and 1.31 g/L) only. Compared with AF, simultaneous AF and MLF significantly elevated the levels of aroma compounds with higher levels of higher alcohols (isoamyl alcohol, active amyl alcohol, isobutyl alcohol, and 2-phenylethyl alcohol), acetate esters (ethyl acetate, isoamyl acetate), and ethyl esters (ethyl octanoate, ethyl dodecanoate). All the endogenous volatile sulfur compounds decreased to trace or undetectable levels at the end of fermentation. MLF accentuated the reduction of acetaldehyde and sulfides. The initially absent dipropyl disulfide was formed, then catabolized, especially in simultaneous AF and MLF. This study suggested that the simultaneous AF and MLF of non-Saccharomyces and LAB could modify the volatile compositions and potentially modulate the organoleptic properties of durian wine.

Induction of simultaneous and sequential malolactic fermentation in 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.

Assessment of volatile and non-volatile compounds in durian wines fermented with four commercial non-Saccharomyces yeasts.

BACKGROUND: Chemical compositions of durian wines fermented with Metschnikowia pulcherrima Flavia, Torulaspora delbrueckii Biodiva, Pichia kluyveri FrootZen and Kluyveromyces thermotolerans Concerto were investigated. RESULTS: Sucrose was not utilized by M. pulcherrima and P. kluyveri, resulting in little formation of ethanol (0.3-0.5%, v/v), while about 7% ethanol was produced by the other two yeasts. Volatiles such as esters and sulfur-containing compounds were synthesized or catabolized and distinctive differences existed among yeasts. Larger amounts of higher alcohols and ethyl esters were detected in wines fermented by T. delbrueckii and K. thermotolerans, whereas M. pulcherrima and P. kluyveri produced more acetate esters such as ethyl acetate (1034.43 and 131.05 mg L(-1) respectively) and isoamyl acetate (0.56 and 27.68 mg L(-1) respectively). Most endogenous sulfur volatiles such as disulfides declined to trace levels, but new ones such as thioesters were formed. Sulfur volatiles in wines fermented by T. delbrueckii accounted for 0.20% relative peak area (RPA), followed by K. thermotolerans (0.23% RPA), P. kluyveri (1.43% RPA) and M. pulcherrima (4.16% RPA). CONCLUSION: The findings showed that a more complex flavor could result from fermentation with different non-Saccharomyces yeasts and the typical durian odor would still remain.

Yeast ratio is a critical factor for sequential fermentation of papaya wine by Williopsis saturnus and Saccharomyces cerevisiae.

The growth kinetics and fermentation performance of Williopsis saturnus and Saccharomyces cerevisiae at ratios of 10:1, 1:1 and 1:10 (W.:S.) were studied in papaya juice with initial 7-day fermentation by W.saturnus, followed by S. cerevisiae. The growth kinetics of W. saturnus were similar at all ratios, but its maximum cell count decreased as the proportion of S. cerevisiae was increased. Conversely, there was an early death of S. cerevisiae at the ratio of 10:1. Williopsis saturnus was the dominant yeast at 10:1 ratio that produced papaya wine with elevated concentrations of acetate esters. On the other hand, 1:1 and 1:10 ratios allowed the coexistence of both yeasts which enabled the flavour-enhancing potential of W.saturnus as well as the ethyl ester and alcohol-producing abilities of S. cerevisiae. In particular, 1:1 and 1:10 ratios resulted in production of more ethyl esters, alcohols and 2-phenylethyl acetate. However, the persistence of both yeasts at 1:1 and 1:10 ratios led to formation of high levels of acetic acid. The findings suggest that yeast ratio is a critical factor for sequential fermentation of papaya wine by W.saturnus and S. cerevisiae as a strategy to modulate papaya wine flavour.

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

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.