Assessment of biological properties and applications of extracts obtained from agroindustrial subproducts

Abstract

Lipid oxidation and microbial growth, two of the most well studied processes associated with food spoilage, become the focus of attention when natural compounds are used to circumvent the problem. Synthetic antioxidants associated with food matrices always had a negative connotation due to the undesirable effects related with their consumption over long periods of time. Nevertheless, the addition of natural compounds with antioxidant activity has gained a great importance, particularly when these compounds, less harmful and from renewable resources, can block both processes. In this work, four extracts obtained from by-products / industrial residues were utilized to evaluate: the antioxidant and the antimicrobial activities, the ability to enhance the growth of probiotic bacteria and the applicability associated with the food industry. Grape pomace (GP) extract was the one with the highest antioxidant activity whereas the extract from almond shells (AS) was the one with the lowest capacity. The identification of the compounds present in the extracts showed different profiles for all extracts although there were common compounds, such as: vanillic acid, 3,4-dihydroxybenzaldehyde, vanillin, quercetin, hydroxymethyfurfural and 2-furfuraldehyde. Concerning the antimicrobial activity, all the extracts inhibited the growth of pathogenic bacteria, namely Escherichia coli, Pseudomonas aeruginosa, Listeria monocytogenes, Staphylococcus aureus and Salmonella spp. However, no trend was observed, i.e., the extracts did not show a selective action upon either Gram-positive or Gram-negative bacteria. From the analysis of the minimum bactericidal concentrations (MBCs), the eucalypt wood (EW) extract was the most active, whereas the AS and CC (corn cobs) extracts were less active. The time-kill analysis/ survival curves have highlighted the antimicrobial effect of the extracts; however, this was not immediate, in that for the majority of cases, this effect only occurred at approximately 24h. The assays with probiotic bacteria showed that the tested extract concentrations (0.025% and 0.1%) did not significantly affect the growth of these microorganisms. Finally, for the application associated with the food industry, films with the extracts were produced, and their characterization did not evidence strong differences; statistically significant differences were only observed for color and moisture content, with the AS and CC extracts showing smaller values comparatively to the other films. In addition, all films showed antimicrobial activity against the pathogenic bacteria tested, suggesting the possible use of these extracts in an edible film.

Date of Award	22 Oct 2014
Original language	English
Awarding Institution	Universidade Católica Portuguesa
Supervisor	Freni Tavaria (Supervisor), Patricia Gullón Estévez (Co-Supervisor) & Ana Maria Gomes (Co-Supervisor)