Comprehensive Utilization of Electro-Activated Whey-Based Media in the Cell Growth, Metabolites Production and Aroma Compounds Synthesis Using a Starter Culture Originated from Kefir Grain

Abstract

Whey and whey permeate (WP) are the main by-products from cheese or casein manufacturing process and there is a serious demand of developing a sustainable approach for their utilization to evade environmental pollution. The objective of this study was to explore the feasibility of using electro-activated (EA) whey-based substrates (whey, WP, lactose) as carbon sources to produce valuable metabolites including organic acids (i.e., lactic, acetic, citric, and propionic acids), exopolysaccharides (kefiran), and volatile flavour compounds using the whole kefir grains as a starter culture. Fermentation was performed by inoculating a mixed microbiota from kefir grains in EA and non-EA solutions of lactose, whey, and WP and were statically incubated for 96 h at 30 ℃. The results showed that the EA substrates achieved a higher biomass growth in a reduced fermentation time than their non-EA mediums. The highest cell growth (6.04 g/L) was obtained for EA-whey after 72 h which was even 1.7-fold higher than a standard nutrition broth, the reinforced clostridial medium (RCM). Furthermore, EA-whey produced a maximum of 8.46, 3.97, 0.60, and 1.02 g/L of lactic, acetic, citric, and propionic acid, respectively. Moreover, EA-whey achieved the highest kefiran production of 2.99 g/L, followed by the whey (2.67 g/L), EA-WP (2.31 g/L), WP (1.88 g/L), RCM broth (1.42 g/L), EA-lactose (1.37 g/L), and lactose (0.91 g/L). The results also demonstrated that various aromatic volatile compounds were produced during the fermentation of EA-whey, which may increase the organoleptic characteristic/sensory quality of the fermented products. Thus, the results of the present study provide a strong evidence that the EA-substrates, especially EA-whey, could be potential feedstock to develop an efficient bioprocess for producing valuable metabolites using kefir grains as a suitable starter.