Impact of Thermal Processing on Taste Development in Food

Abstract

Despite the increasing demand, healthier foods suffer from lower consumer acceptability due to inferior flavor quality. The flavor of food is greatly affected by the food composition and thermal processing. This study specifically investigates the thermal processing impact on the positive and negative taste attributes of foodstuffs, which enables the optimization of processing strategies to improve the palatability and ultimately the consumption of ‘healthier’ formulated food products. The overall goal of this work was to characterize the effect of thermal processing on the taste-active compounds or the generation of taste modulating compounds in foodstuffs. This work mainly focuses on the influence of three common thermal processing techniques on the resulting taste profiles in three food systems respectively: the roasting of cocoa, the extrusion of corn cereal, and the frying of potato chips. These three processing techniques are widely utilized by the food industry. Bitterness was investigated in roasted cocoa and extruded whole grain corn while umami was characterized in deep fried potato chips. The influence of roasting on the taste attributes of cocoa was studied first. Roasting processes involve the Maillard reaction, which is a ubiquitous thermally catalyzed chemical pathway that is well-known to impact aroma development as well as taste, such as bitterness. Bitterness is a challenge for consumer acceptability, which is typically masked by adding sugar. The goal of this part of the research was to discover the impact of Maillard chemistry on endogenous bitter-tasting compound, catechin, in raw cocoa, and likewise on the resulting bitter taste profile of the roasted beans. Catechin-Maillard reaction products were identified by stable isotope labeling techniques in model reactions using the simulated cocoa roasting conditions. Eight reaction products were identified and reported for the first time. One of the newly-identified compounds significantly suppressed the perceived bitter intensity of the caffeine solution, which is a novel bitter blocker. Further analysis revealed that this bitter blocking compound was present in both the raw and roasted cocoa beans; however its concentration was higher in roasted cocoa beans. A generation mechanism of the bitter blocker was proposed. The results of the first phase indicated that the bitter profile of cocoa beans was altered by thermal reactions of the endogenous bitter compounds. In the second research phase of this study, the influence of extrusion on the taste profile of puffed whole grain corn products was examined. The goal of this phase is to identify the key bitter compounds and understand how they are influenced by extrusion. Three phenolic compounds (chaenorpine, coumaryl-spermidine, terrestribisamide) and one amino acid (L-tryptophan) were identified as the main bitter compounds in the extruded whole grain corn product. Based on sensory recombination analysis, chaenorpine was found to have the highest contribution to the bitterness intensity, based on the concentration of the bitter compounds reported in the saliva during mastication. Additionally, all of the identified bitter compounds were found to be degraded during extrusion, suggesting that the further optimization of extrusion could be utilized to suppress bitterness in order to improve the flavor quality of whole grain extruded products. In the last phase of this research project, the role of the thermal process, deep frying, on the taste profile of potato chips was examined. Potato chips are a highly desired food product and the umami taste is well known to positively contribute to the taste profile. Initial analysis indicated that the umami taste attribute of potato chips increases with frying time thus the compounds that contribute to umami were characterized. A dehydration product of monosodium glutamate (MSG), monosodium L-pyroglutamate (L-MSpG) and monosodium D-pyroglutamate (D-MSpG) were identified for the first time as umami enhancing compounds that contributed to the umami flavor of potato chips. The generation of pyroglutamates was reported to be directly related to the frying time. Sensory time-intensity taste analysis of potato chips with topical added L-MSpG and D-MSpG revealed significantly higher umami intensity and the overall higher potato chip flavor intensity. In summary, the impact of three thermal processes on taste profile was studied in three different food products. This study provides a novel basis for flavor optimization by investigating the thermal impact on taste chemistry. The ultimate goal of this study is to increase the market demand for health conscious foods, thus benefiting the food industry as well as promoting a healthy lifestyle.