Stability and Activity of β-Galactosidase in Sonicated Cultures of Lactobacillus delbrueckii ssp. bulgaricus 11842 as Affected by Temperature and Ionic Environments

Investigation into the use of novel pretreatments in the fermentation of Alaria esculenta by Lactiplantibacillus plantarum and kombucha SCOBY

High pressure processing (HPP), ultrasound probe (USP) and ultrasound bath (USB) were applied to Alaria esculenta as a fermentation pre-treatment. Seaweed was then fermented by Lactiplantibacillus plantarum (LAB) or symbiotic culture of bacteria and yeast (SCOBY). Physiochemical properties of fermented seaweed were measured. pH was significantly different (p < 0.05) across SCOBY-fermented samples with different pre-treatments but not LAB-fermented samples (p > 0.05). There was a significant difference (p < 0.05) in total viable count (TVC) with the highest count in HPP-treated samples, and lowest in control samples. Organic acids differed significantly (p < 0.05) across pre-treatments for both fermentation groups. 27 volatile compounds were detected in the samples, with alcohols and ketones the most prominent groups. The quantity of volatile compounds was not significantly lower (p > 0.05) from seaweed powder. The control sample had the highest levels of tropomyosin (15.92 mg/kg) followed by HPP samples.

Fermentation at non-conventional conditions in food- and bio-sciences by the application of advanced processing technologies

The interest in improving the yield and productivity values of relevant microbial fermentations is an increasingly important issue for the scientific community. Therefore, several strategies have been tested for the stimulation of microbial growth and manipulation of their metabolic behavior. One promising approach involves the performance of fermentative processes during non-conventional conditions, which includes high pressure (HP), electric fields (EF) and ultrasound (US). These advanced technologies are usually applied for microbial inactivation in the context of food processing. However, the approach described in this study focuses on the use of these technologies at sub-lethal levels, since the aim is microbial growth and fermentation under these stress conditions. During these sub-lethal conditions, microbial strains develop specific genetic, physiologic and metabolic stress responses, possibly leading to fermentation products and processes with novel characteristics. In some cases, these modifications can represent considerable improvements, such as increased yields, productivities and fermentation rates, lower accumulation of by-products and/or production of different compounds. Although several studies report the successful application of these technologies during the fermentation processes, information on this subject is still scarce and poorly understood. For that reason, the present review paper intends to assemble and discuss the main findings reported in the literature to date, and aims to stimulate interest and encourage further developments in this field.

Lactobacillus reuteri β-galactosidase activity and low milk acidification ability

β-galactosidase activity was studied as a possible cause of the low milk acidification ability observed in Lactobacillus reuteri NRRL 14171. Enzymatic activity was determined in MRS broth supplemented with either glucose or lactose and milk at the middle and final stage of the exponential phase, as well as at the stationary phase. Results were compared with β-galactosidase activity in Lactobacillus casei NRRL-B1922, a strain that shows the milk acidification ability. The effects of the types of carbon and nitrogen sources were established by comparison of growth parameters (higher maximum cell concentration and specific growth rate) in broth culture and skim milk supplemented with 2% glucose or 1% casein peptone. In milk, L. reuteri showed higher β-galactosidase activity in all growth phases compared with L. casei. Greater cell concentration maxima, specific growth rates, and acidification abilities were observed in L. reuteri when it was cultured in milk supplemented with 1% casein peptone compared with non-supplemented milk cultures. Results suggest that the poor milk acidification ability observed in L. reuteri may be more related to a weak proteolytic system than to deficient β-galactosidase activity.Key words: Lactobacillus reuteri, growth parameters, β-galactosidase, acidification.