Optimization of fermentation processes for the production of indigenous fruit wines (Marula)

[摘要] ENGLISH ABSTRACT:The importance of indigenous fruit wines is not well researched and documented. Thereis a need to develop and exploit these valuable food resources through improvedproduction practices, storage, preservation and utilization technologies. The maruia fruitis beneficial in many ways, it can be used for making juice, jam, beer or can be eaten asa whole fruit. The highly nutritive nature of the fruit, its distinctive tropical flavor, its wildoccurrence and demand by the local and international communities for the by-productsof the fruit necessitated efforts to optimize the technological processes for theproduction of the possible by-products. This study focuses on the fermentationtechnology of the maruia fruit.The effect of enzymes prior to the fermentation process and post-fermentationwas evaluated. For pre-fermentation processes we focused on the ability of commercialenzymes to increase juice yield, improve the clarification and filterability. For pre- andpost-fermentation applications, aroma release was considered. The results indicated asignificant increase in the yield depending on the enzyme used. An increase of at least2% was recorded and a maximum of 12% yield increase was observed. The enzymesalso had a phenomenal effect on the release of bound monoterpenes and henceenhancing the flavor of the juice. The panel of judges confirmed the results from the gaschromatography analyses by noting an increase in flavor intensity in the enzyme treatedjuice.The possibility of selecting a yeast strain that performs best during thefermentation of maruia pulp was also looked at. This study aimed at selecting a strainthat produces wine and distillate with the typical maruia flavor complex. We showed theeffect of the different yeast strains, in the wines and distillates, on the principal volatilecompounds. We then correlated the performance of the different strains as perceived bythe panel to the various volatile compounds. The effect of fermentation temperature onthe performance of the different yeast strains was also considered. Fermenting themaruia pulp at different temperatures resulted in the production of wines and distillateswith different volatile profiles for the different yeast strains. The wines and distillatesfermented at a low temperature of 15°C were preferred to the wines and distillatesfermented at 30°C. However, not all strains performed well at 15°C, strains like NT116performed better at 30°C. The different commercial strains produced wines anddistillates with significantly different flavor profiles. These differences in the flavor profileswere reflected in the sensory evaluation where, depending on the interaction of thevolatile compounds some wines and distillates were preferred to others. The effect of thedifferent commercial enzymes and yeast strains should thereof be further evaluated andoptimized on a larger scale. This would greatly help prevent variation in quality of thefermented by-products of the maruia fruit.

[发布机构] Stellenbosch University