Colucci Cante, Rosa (2021) Development of processes for the production of postbiotic functional foods. [Tesi di dottorato]

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Several techniques were developed in order to enhance the content of bioactive compounds or promote their production in food products. Lactic acid fermentation is one of the most important food processing technologies used to produce functional probiotic foods. A novel category of fermented functional foods is gaining increasing interest and is represented by postbiotic products, consisting of inactivated microorganisms and molecules (enzymes, peptides, organic acids) produced in the final or intermediate stage of the metabolic process of these probiotic bacteria. Although postbiotics do not contain live microorganisms, they show a beneficial health effect through similar mechanisms that are characteristic of probiotics, minimizing the risks associated with their intake. For this reason, they could be considered a safer alternative to clinical application for immune-deficient patients or infants. This research, in collaboration with Kraft Heinz Company, consisted of the development of processes for the production of wet and dried functional foods with a postbiotic effect, intended for categories of people with high pathological vulnerability, such as children, elderly people and pregnant women. The purpose of this project was to investigate the effect of fermentation process, carried out using Lactobacillus paracasei CBA L74, patented by Kraft Heinz, heat treatments and drying processes on the postbiotic properties of the semi-finished products obtained, choosing as raw materials milk, rice flour and leguminous (beans) suspensions. The processes were examined and optimized at laboratory scale and then implemented at pilot scale with a successful and efficient scaling up, except for beans that had been an unexplored food matrix to be fermented until then and required a further optimization of protocols at laboratory scale before performing the trials on the pilot plant. At lab scale, rice and milk fermentation were carried out with and without pH control and in both cases an improvement in the terms of kinetic performance of the process was observed when pH control was implemented. The fermentation process was characterized in terms of bacterial growth (maximum values of 1.9 × 10^8 ± 1.2 × 10^8 CFU/mL after 20 h and 5.3 × 10^8 ± 4.7 × 10^8 CFU/mL after 18 h were achieved for milk and rice flour fermentations, respectively), lactic acid concentration (maximum values of 1.2 ± 0.3 g/L and 4.4 ± 0.21 g/L were achieved after 24 h of fermentation process for milk and rice flour, respectively) and production of a selected functional metabolite, considered as responsible of the immunomodulatory activity of the postbiotics obtained (6.93 ± 0.5 mg/L and 17.23 ± 0.28 mg/L after 24 h of fermentation, for milk and rice flour,respectively). An aqueous suspension of cooked beans was fermented without pH control in two different mixing conditions. The mixing system was improved by designing an impeller that guarantees a higher homogeneity of the medium inside the reactor: the results showed better performances in terms of growth rate and lactic acid production, reaching a microbial charge of approximately 1 × 10^9 CFU/mL after 14 h and a lactic acid content of 2 g/L after 16 h of process. The functional peptide was not detected in the fermenting bean suspension, so a further optimization of the protocol will be necessary for this purpose. A thermal treatment at 90°C for 1 min, for rice and milk, and at 90°C for 15 min, for beans, was sufficient to reduce the bacterial charge in the fermented product without negatively affecting the products quality; freeze drying and spray drying technologies had the same impact on the food products, not altering their organoleptic and chemical properties: a promising result since spray drying technology is usually used at larger scale. The results obtained at pilot scale for milk and rice flour were completely overlapped. During milk fermentation, a maximum bacterial load of 6.7 × 10^8 ± 2.65 × 10^8 CFU/mL was reached after 20 h of process; a lactic acid content of 2.1 ± 0.25 g/L and a peptide concentration of 14.20 ± 0.80 mg/L were observed at the end of fermentation. As for rice flour, a maximum bacterial growth of 1.27 × 10^9 ± 6.9 × 10^8 after 18 h of process, a maximum lactic acid production of 6.03 ± 0.7 g/L after 24 h and a maximum functional peptide content of 22.60 ± 4.10 mg/L after 20 h of fermentation were obtained. For both scales, rice flour fermentation gave better results in terms of bacterial growth, lactic acid and functional peptide production, probably for the rice prebiotic components. Also, at pilot scale, a thermal treatment of 90°C for 1 min was sufficient to reduce the bacterial charge in the fermented products and it was confirmed that spray drying technology had a low impact on the product. Moreover, a shelf-life analysis of the products obtained at pilot scale was performed at three different storage temperatures (4°C, 20°C and 37°C) for six months to evaluate the food product stability over time: dried fermented rice resulted more stable than milk.

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