Glycosidically bound aroma precursors in fruits: A comprehensive review.

Fruit aroma is mainly contributed by free and glycosidically bound aroma compounds, in which glycosidically bound form can be converted into free form during storage and processing, thereby enhancing the overall aroma property. In recent years, the bound aroma precursors have been widely used as flavor additives in the food industry to enhance, balance and recover the flavor of products. This review summarizes the fruit-derived aroma glycosides in different aspects including chemical structures, enzymatic hydrolysis, biosynthesis and occurrence. Aroma glycosides structurally involve an aroma compound (aglycone) and a sugar moiety (glycone). They can be hydrolyzed to release free volatiles by endo- and/or exo-glucosidase, while their biosynthesis refers to glycosylation process using glycosyltransferases (GTs). So far, aroma glycosides have been found and studied in multiple fruits such as grapes, mangoes, lychees and so on. Additionally, their importance in flavor perception, their utilization in food flavor enhancement and other industrial applications are also discussed. Aroma glycosides can enhance flavor perception via hydrolyzation by ß-glucosidase in human saliva. Moreover, they are able to impart product flavor by controlling the liberation of active volatiles in industrial applications. This review provides fundamental information for the future investigation on the fruit-derived aroma glycosides.

Optimizing extraction method of aroma compounds from grape pomace.

Grape pomace is a major wine industry byproduct. Extraction of volatile compounds from grape pomace is rarely explored. A cost-effective method was developed in this study for aroma compounds extraction from grape pomace with the potential for industrial application. Based on the solvent extraction procedure, experimental factors including pretreatment, enzymatic hydrolysis time, solvent concentration and distillation time were investigated to optimize the extraction process. Volatile compounds of the pomace extract were analyzed using headspace solid-phase microextraction gas-chromatography mass spectrometry (HS-SPME-GC-MS) method. Results revealed that enzymatic hydrolysis was the optimal pretreatment method. A maximum extraction efficiency was achieved under 48 hr of enzymatic hydrolysis, 70% of ethanol concentration and 20 min of distillation. A total of 65 volatile compounds were identified in the extract, including 16 alcohols, 1 alkane, 1 aldehyde, 9 esters, 3 ketones, 4 phenols, 6 terpenes, and 1 furan, of which 15 volatiles were determined as odor-active compounds. This study developed a feasible extraction technique to recycle the underutilized byproducts from wine industry to produce aroma/flavor food additives. PRACTICAL APPLICATION: This study develops a cost-effective method for aroma compounds extraction from grape pomace with the potential for industrial application as food additives.