Philip Curran

Chemical composition and sensory profile of pomelo (Citrus grandis (L.) Osbeck) juice.

Two cultivars (Citrus grandis (L.) Osbeck PO 51 and PO 52) of Malaysian pomelo juices were studied by examining their physicochemical properties (i.e. pH, °Brix and titratable acidity), volatile and non-volatile components (sugars and organic acids). Using solvent extraction and headspace solid-phase microextraction, 49 and 65 volatile compounds were identified by gas chromatography-mass spectrometer/flame ionisation detector, respectively. Compared to pink pomelo juice (cultivar PO 52), white pomelo juice (cultivar PO 51) contained lower amount of total volatiles but higher terpenoids. Descriptive sensory evaluation indicated that white pomelo juice was milder in taste especially acidity. Furthermore, principal component analysis and partial least square regression revealed a strong correlation in pomelo juices between their chemical components and some flavour attributes (i.e. acidic, fresh, peely and sweet). Hence, this research enabled a deeper insight into the flavour of this unique citrus fruit.

Coffee fermentation and flavor--An intricate and delicate relationship.

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.

Fermentation of three varieties of mango juices with a mixture of Saccharomyces cerevisiae and Williopsis saturnus var. mrakii.

This study was carried out to ascertain the behavior and fermentation performance of mixed yeasts in mango juices of three varieties. Saccharomyces cerevisiae MERIT.ferm and Williopsis saturnus var. mrakii NCYC500 at a ratio of 1:1000 were simultaneously inoculated into juices of three mango (Mangifera indica L.) varieties (R2E2, Harum Manis and Nam Doc Mai). Both yeasts grew well in all juices and there was no early growth arrest of either yeast, but there was late death of W. saturnus var. mrakii NCYC500 in the Nam Doc Mai juice. Fructose, glucose and sucrose were consumed to trace levels in all juices. Changes in citric, tartaric, malic, acetic and succinic acids varied with mango varieties. While the changes of major volatiles were similar in all varieties, there were significant varietal differences in the volatile composition of the resultant mango wines. The volatiles, especially most of the terpenes, of the juices decreased drastically and new volatiles such as β-citronellol were formed. R2E2 wine had more fruity, sweet and creamy notes, and retained more of its original character due to a higher retention of ketones/lactones. Harum Manis wine had the lowest aroma intensity with more green and terpenic notes associated with higher levels of residual terpenes than the other two varieties. Nam Doc Mai wine possessed the highest aroma intensity with winey, yeasty, fruity and floral notes attributed to higher amounts of alcohols, acetate esters and ethyl esters. These findings may help develop different styles of mango wine.

Characterisation of calamansi (Citrus microcarpa). Part II: Volatiles, physicochemical properties and non-volatiles in the juice

Calamansi juices from three countries (Malaysia, the Philippines and Vietnam) were characterised through measuring volatiles, physicochemical properties and non-volatiles (sugars, organic acids and phenolic acids). The volatile components of manually squeezed calamansi juices were extracted using dichloromethane and headspace solid-phase microextraction, and then analysed using gas chromatography-mass spectrometry/flame ionisation detector, respectively. A total of 60 volatile compounds were identified. The results indicated that the Vietnam calamansi juice contained the highest amount of volatiles. Two principal components obtained from principal component analysis (PCA) represented 89.65% of the cumulative total variations of the volatiles. Among the non-volatile components, these three calamansi juices could be, to some extent, differentiated according to fructose and glucose concentrations. Hence, this study of calamansi juices could lead to a better understanding of calamansi fruits.

Characterisation of calamansi (Citrus microcarpa). Part I: Volatiles, aromatic profiles and phenolic acids in the peel

Volatile compounds in the peel of calamansi (Citrus microcarpa) from Malaysia, the Philippines and Vietnam were extracted with dichloromethane and hexane, and then analysed by gas chromatography-mass spectroscopy/flame ionisation detector. Seventy-nine compounds representing >98% of the volatiles were identified. Across the three geographical sources, a relatively small proportion of potent oxygenated compounds was significantly different, exemplified by the highest amount of methyl N-methylanthranilate in Malaysian calamansi peel. Principal component analysis and canonical discriminant analysis were applied to interpret the complex volatile compounds in the calamansi peel extracts, and to verify the discrimination among the different origins. In addition, four common hydroxycinnamic acids (caffeic, p-coumaric, ferulic and sinapic acids) were determined in the methanolic extracts of calamansi peel using ultra-fast liquid chromatography coupled to photodiode array detector. The Philippines calamansi peel contained the highest amount of total phenolic acids. In addition, p-Coumaric acid was the dominant free phenolic acids, whereas ferulic acid was the main bound phenolic acid.

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

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 24h, pH 6.2 and enzyme amount 0.26 g. Under the optimised conditions, a yield of 14.25mg/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.

Characterization of Volatile Compounds and Aroma Profiles of Malaysian Pomelo (Citrus grandis (L.) Osbeck) Blossom and Peel

Abstract The knowledge of the chemical compositions and sensory profiles of their peels and blossoms could lead to better understanding of two cultivars of Malaysian pomelo. This work was to determine the volatile compositions of Malaysian pomelo blossoms and peels through HS-SPME-GC/MS analysis and principal component analysis (PCA) approach as well as to identify their key aroma profiles by sensory evaluation. Pink and white pomelo blossoms contained similar volatiles, which mainly consisted of limonene, cis-β-ocimene, α-terpinene, linalool, methyl anthranilate, and indole. Their primary difference was in the concentration ratio between limonene and linalool. Major volatiles in pomelo peels were terpene hydrocarbons. Pink pomelo peel contained higher levels of aldehydes (e.g. octanal, decanal and citral), while some trace-level important compounds (e.g. β-sinensal, α-sinensal and nootkatone) were found only in white pomelo peel. Through sensory evaluation, both intact pomelo blossoms had similar aroma profiles, which comprised the dominant note of floral, followed by animalic and citrus blossom. Additionally, pink pomelo peel extract was much more impactful than white pomelo peel extract, especially in grapefruit and green notes. Through HS-SPME-GC/MS and PCA, the authors managed to discover the similarities and differences between two Malaysian pomelo cultivars. Further, the sensory data on intact pomelo blossoms and pomelo peel extracts provided more insight.

Lipase-catalysed ester synthesis in solvent-free oil system: Is it esterification or transesterification?

Ester synthesis was carried out in a solvent-free system of lipase, coconut oil and ethanol or fusel alcohols to ascertain the reaction mechanism. During ester formation, octanoic and decanoic acids increased initially and then decreased gradually, indicating that ester production was a two-step reaction consisting of hydrolysis and esterification, rather than alcoholysis. With ethanol as the alcohol substrate, added butyric acid inhibited ester synthesis. However, when fusel alcohols were used as the alcohol substrate, no significant inhibitory effect by butyric acid was observed. Added octanoic acid did not show any adverse effect on the synthesis of corresponding esters. The results suggest that polarity of the reactants determines lipase activity. This study provides the first evidence on the mechanism of immobilised lipase-catalysed ester synthesis in a solvent-free system involving both hydrolysis and esterification.

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

Effects of Pure and Mixed-Cultures of Saccharomyces cerevisiae and Williopsis saturnus on the Volatile Profiles of Grape Wine

Non-Saccharomyces yeasts are being recognised for their ability to produce wines with unique character. This study assessed the production of volatiles by co-inoculating Saccharomyces cerevisiae and Williopsis saturnus. Laboratory-scale fermentations were carried out using pure and mixed-cultures of S. cerevisiae and W. saturnus at a ratio of 1:1000. The mixed-culture fermentation was dominated by S. cerevisiae, while W. saturnus had an early growth arrest. Changes of oenological parameters and volatiles were similar in both the mixed- and the S. cerevisiae monocultures. A range of volatiles was formed with alcohols and esters constituting the majority of volatiles produced. Volatiles initially present in the grape juice, particularly (E)-2-hexen-1-ol, 1-hexanol, trans-2-hexenal and n-hexanal, were metabolized. Wines produced using mixed-cultures closely resembled those fermented by the S. cerevisiae monoculture but acquired minor flavor characteristics from the initial presence of W. saturnus. These findings suggest that the ratio of S. cerevisiae and W. saturnus is critical to the survival of the non-Saccharomyces yeast and the impact on the perceivable characteristics of the resultant quality and flavor of wines.