Sustainable production of postbiotics for food applications

Abstract

Food is an essential need of human life and has nutrients that support growth and health. In recent decades, functional foods with ingredients such as probiotics, prebiotics and postbiotics have gained much attention among consumers. Postbiotics are defined as "a preparation of inanimate micro-organisms and/or their components that confers a health benefit to the host". Postbiotics are functional bioactive compounds generated through the fermentation of lactic acid bacteria, such as Lactobacillus plantarum and fermentum and/or the yeast Saccharomyces cerevisiae. The most studied metabolites derived from postbiotics are short chain fatty acids, extracellular polysaccharides, cell lysates, theicoic acid and vitamins. They also have several biological properties such as anti-inflammatory, immunomodulatory, antihypertensive, anti-proliferative and antioxidant. The objective of this work was the use of sugar cane by-products (bagasse and straw) as a source of sugar after fermentation with L. planta rum and S. cerevisiae as a sustainable alternative for food applications. For the by-products to produce post-biotic extracts it was necessary to perform saccharification and fermentation. The saccharification conditions were optimised by testing the enzymes celluclast and xylanase, different reaction times (24 and 48 h) and the impact of milling the biomass. A simultaneous saccharification and fermentation with different microorganisms (L. plantarum, fermentum and S. cerevisiae) was performed. In a second phase, sequential saccharification and fermentation was tested with L. plantarum for 48 h and S. cerevisiae for 72 h, with removal of biomass after saccharification and of intact cells at the end of the fermentation. The extracts were characterised at an initial stage for potential screening with respect to their antioxidant and antimicrobial activities, and the final extracts obtained by improving the process conditions were characterised for prebiotic and antidiabetic potential, total protein, total phenolic content and compounds, the profile of organic acids and monosaccharides and the immunomodulatory effect and cytocompatibility. The main results obtained in the initial phase show that the nonfermented extracts have greater antioxidant activity than the fermented extracts with the Lactobacillus strains, while with the Saccharomyces yeast the fermented extracts have better antioxidant activity than the non-fermented ones. Regarding the antimicrobial activity, the fermented extracts did not inhibit the growth of food pathogenic bacteria. Monosaccharides were identified in the final extracts in the unfermented extracts and acetic acid was identified in all the extracts analysed. Total protein is similar in all extracts ranging from 32-38%. The straw extract fermented with Saccharomyces yeast had the highest phenolic content (16.15 mg GA/ g dw). Six phenolic compounds were identified and the predominant ones were p-coumaric acid and 4-hydroxybenzaldehyde and the most predominant organic acid was acetic acid. The fermented extracts showed a good capacity to reduce the pro-inflammatory mediators in Caco-2 cells. The prebiotic potential of the two extracts did not show great impact in Lactobacillus and Bifidobacterium, although they increased over time the short chain organic acids (SCFA) with greater incidence in acetate, butyrate and propionate. Thus, the postbiotics produced by yeast and bacteria show potential in chemical and biological properties for use in the food and nutraceutical area.

Date of Award	20 Jul 2023
Original language	English
Awarding Institution	Universidade Católica Portuguesa
Supervisor	Ana Raquel Madureira (Supervisor), Ana Lúcia Silva Oliveira (Co-Supervisor) & Carla Oliveira (Co-Supervisor)