D'souza, Derrick (2025) The Molecular basis of savoury. PhD thesis, Victoria University.

Abstract

It is widely portrayed that health, sustainability and environmental concerns are driving consumers to choose a plant-based diet. However, they do form supplementary contributors to food choices, amongst other factors. Flavour ultimately decides whether a food will be acceptable at the point of consumption. Other than for the small percentage of neophobes, most of the world's growing middle class make themselves acquainted with the latest diet fads, as observed through the decades. If we are to stay on this path of promoting and advocating plant-based diets as healthy, sustainable, and environmentally friendly, it only seems pertinent that we deliver flavoursome products that are appreciated by most so that they remain trendy. After over a hundred years of being discovered, umami now forms the buzzword of the decade. However, it was observed that umami was only partially responsible for the appreciation of beef in high-temperature short-time (HTST) cooked foods such as grilled and fried burgers. Rather, the rapidly formed aroma volatiles from precursors are involved in simultaneous oxidation degradation and interaction with the Maillard reaction products (SODIM) process. This includes contributions from a myriad of seasonings and herbs added to meat during cooking, increasing its appreciability. Giving ‘mirepoix’ (pronounced ‘meer pu ah’) its fair dues, we ought to characterize the formation of aroma compounds in beef during HTST processing compared to plant-based products. Although comparisons between beef burgers and plant-based meats have been sought, the studies only compared commercial products. There is compelling evidence that aroma is a critical yet pervasive, if not an all-encompassing, attribute to decision-making in food choice. Thus, this study was conceptualized to observe the formation and development of volatiles in plant-based ingredients and compare them to the aroma profile of beef mince. The key question to be addressed was, how can the aroma of a popular food be captured and analysed objectively? If aromas were based on volatiles. Could they be identified and measured on a molecular basis using chemometrics? More specifically, the study aimed to assess the use of head space Solid-phase Microextraction Gas Chromatography Mass Spectrometry (HS SPME GCMS) as a tool to study aroma profiles. Further, it proposed studying the different constituents of beef mince, namely the fat, sarcoplasm, and myofibrillar fractions, and their ability to promote aroma formation. Finally, it investigated the formation of volatiles in heat-treated plant-based lipids and proteins compared to beef mince in the formation of aromas. The topic's significance is highlighted by the evidence noted in the literature of the challenges observed in the analysis of aroma volatiles. A comprehensive scoping review is presented on the current status of aroma analysis and its interpretation of volatile compounds found in plant-based meat and their likeness to animal meat. The key findings of the review suggest that the lack of standard definitions of common terms exacerbates differences in opinion. However, using advanced untargeted chemometric analysis may be able to observe, decipher and guide researchers and flavour chemists to be objective in creating appreciable plant-based foods. Consequently, the importance of the methods of analysis using chemometrics highlighted the need for optimising analytical conditions. The application of HS-SPME-GCMS was chosen as a green technology with the ability to analyse wide-ranging volatiles from complex matrices. Due to the varied adsorption capability of the fibres, initially, both Divinylbenzene/Carboxen/Polydimethylsiloxane (DVB/CAR/PDMS) and Carboxen/ Polydimethylsiloxane (CAR/PDMS) fibres were selected for the study. However, DVB/CAR/PDMS was incorporated in the study due to its ability to adsorb a wider range of volatiles from the headspace. The ability of the fibres to adsorb analytes was observed to be dynamic, depending on a range of factors, with time and temperature being the most effective. control A single time and temperature parameter for equilibration and concentration was observed to optimally extract analytes from the headspace. Volatiles observed from the method of cooking (pan-grilled vs heat treatment in vial) matched closely compared to the formats (Fresh whole vs lyophilised). Although not quantified, peak intensities for aldehydes in vail-cooked lyophilized samples suggest a lower rate of oxidative degradation. In relation to the formation of warmed-over flavours (WoF) and other degradative products during storage, the effect of chilling the sample was more pronounced compared to not chilling or the addition of water prior to analysis. The use of a single internal standard could not be justified due to the number of volatiles observed whilst conducting untargeted analysis. The adsorbability of the internal standard seemed to depend on the headspace environment and concentration of analytes, voiding its application. The complexity of beef warranted its fractionation, as observed from the optimisation study. This enabled the observation of volatile formation in the different fractions. SDS PAGE highlighted two important aspects of fractionation: 1) the presence of many soluble proteins in addition to myoglobin and haemoglobin in the aqueous extract; and, 2) the efficacy of removing soluble proteins observed in the deblooded fraction. The separation enabled the observation of volatile formation from the different fractions. It resulted in five distinct essays with a combination of either the sarcoplasmic, myofibrillar or lipid fractions. All five assays, including the whole meat samples, produced significantly different peaks, as observed from the chromatograms. The largest number of aldehydes were observed in the lipid fraction, followed by the deblooded and defatted myofibrillar fraction. Fresh and lyophilized whole beef mince also presented differences in volatile profiles. Fractionation demonstrated the limitations of analysing volatiles from whole foods. The volatile profiles obtained from heat-treated coconut and canola oils and their admixtures were also significantly different to the volatiles observed from beef fat. Although beef fat is known to possess a high degree of saturated fats, the lipids extracted from beef mince produced volatiles similar to those observed from canola oil. Coconut oil produced the lowest number of volatiles compared to canola oil and beef fat. Volatiles from plant proteins, namely pea and soy, were also compared to those from the myofibrillar fraction of beef mince. Whilst volatiles from heat-treated pea and soy compared favourably with each other, they differed from beef. The largest number of volatiles was observed from pea protein. When proteins and lipids were combined, they followed a similar pattern of volatile formation. The project established a method for objectively analysing aroma formation using chemometrics. It successfully observed the formation of volatile compounds from plant-based ingredients and compared them to volatiles from beef mince. However, the current research has limitations in identifying every molecule and understanding the dynamics that contribute to noticeable flavour differences. Further research could assist our understanding of whether the addition of flavour enhancers, such as yeast extracts and mushrooms, would produce volatiles similar to those found in beef and thereby invoke a similar perception.

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