Evaluating ultrasound pre-treatment as a tool for improving the process of a fermented beverage made from pineapple by-products

Abstract Fermentation has the potential of converting fruit by-products into value-added products via an efficient, sustainable, and low-cost process. Traditionally, Mexicans use pineapple residues to produce a fermented beverage called tepache. As this soft drink is increasingly consumed in restaurants, it is necessary to develop an effective and reliable process to yield a final product with desirable physicochemical properties. In this work, tepache was prepared using an ultrasound pre-treatment to enhance the fermentation process and improve the end-product quality. The ultrasound was provided by a probe (25 kHz, 400 W) submerged in pineapple preparations before fermentation. Characterization of physicochemical properties was performed on samples processed under different types of amplitude (20 and 100%) and sonication time (5 and 10 min). In all samples, the pH, acidity, and ºBrix values were similar to those in commercial tepaches. On the other hand, microscopy revealed that 5 min of sonication induced positive changes in the suspended matter responsible for the physical stability of fruit beverages. The tepaches obtained with this method had color uniformity. Indeed, 5 min of sonication at the highest amplitude (16.34 kJ・cm-2) augmented the soluble solids during the initial phases of fermentation. Moreover, the results from IR spectroscopy proved that ultrasound helped the ethanol release from yeasts. The maximum ethanol yield, calculated by model fitting, had a positive variation of 35%. These findings prove that ultrasound is capable to induce physicochemical changes useful for the industrial production of tepache.