Development and characterization of functional ingredients through valorization of pineapple by-products
: production, bioactivity and potential application

Student thesis: Doctoral Thesis

Abstract

Fruit processing industries produce huge amounts of wastes, being pineapple by-products one of the most important, due to the fruit size and since 60% (w/w) of pineapple is discarded as waste in normal processing. The application of total valorization of pineapple by-products through green chemistry and sustainable technologies, aiming to achieve ZERO waste, is one of the possible approaches to perform an integrated valorization of these by-products through biorefinery concept. The main objective of this Ph.D. research work was to use pineapple by-products in the development of functional ingredients such as enzymes concentrates, prebiotic/ antioxidant concentrates and functional flours, and to characterize and validate biological activities and technological properties of these new ingredients. First, pineapple stems and peels were fractionated generating two crudes juices (liquid fraction) and two solid fractions (press cakes). Stem and peel liquid fractions represented in weight ca. 5% (w/w) and ca. 17% (w/w) of the total pineapple, respectively. Both liquid fractions contain high content of simple sugars, stem liquid fraction ca. 65% and peel liquid fraction of 67% and less than 1% of soluble dietary fibre in both by-products. Moreover, high content of total phenolic compounds was found ca. 1.3% for stem liquid fraction and 0.7% for peel liquid fraction; both fractions also contained high amounts of total vitamin C, which was corroborated by the high antioxidant activity values of ABTS and ORAC assays. On the other hand, the weight of stem press cake represented ca. 44% (w/w) and peel press cake ca. 38% (w/w) of total pineapple, containing very different proportions of carbohydrates. Stem press cake contained ca. 23% (w/w) of simple sugars, ca. 5% (w/w) of soluble dietary fibre and ca. 45% (w/w) of insoluble dietary fibre, while peel press cake, contained ca. 28% (w/w) of simple sugars, ca. 8% (w/w) of soluble dietary fibre and ca. 38% (w/w) of insoluble dietary fibre, showing to have a great potential as a fibre-rich ingredient. Structural carbohydrates composition showed differences mainly for total cellulose content and for insoluble lignin. A green precipitation methodology was applied to pineapple liquid fractions to extract pineapple enzyme – bromelain, an important natural enzyme widely applied in different industries. The developed methodology, based on precipitation with carrageenan, represents an alternative to traditional separation methodologies. An optimization experimental model was applied to pineapple by-products to define the accountable ranges of bromelain separation. High recover yield of active bromelain (ca. 80%) was achieved for both crude juices making possible to obtained ca. 0.26 g of bromelain from 100 g of pineapple by-products using low polysaccharide concentrations (0.2-0.3% w/v). The remaining stem and peel liquid fractions (after enzyme extraction) were submitted to simulated gastrointestinal tract (GIT) conditions. High degree of digested carbohydrates was observed, since carbohydrates of high molecular weight, after mouth and duodenal stages were transformed in smaller molecules of tri-, di- and monosaccharides. The total content of polyphenols increased throughout the GIT, as well as, the antioxidant activity measured by ABTS and ORAC assays, occurring such burst due to the release of polyphenols linked to other molecules. Polyphenols composition showed that chlorogenic acid is present at highest concentration for both fractions, combined with others, such as caffeic, coumaric and ferulic acids mainly released during GIT digestion. The stem fraction was selected to evaluate prebiotic activity, revealing relevant activity upon five probiotic strains (two strains of lactobacilli and three bifidobacteria). The impact of each stage of GIT simulation upon prebiotic activity was measured, showing that the activity slightly reduced throughout the simulated digestion, but still modulated the growth and metabolism of probiotic strains. The solid fractions (peels and stems) were also submitted to the simulation of the gastrointestinal tract to understand the impact of digestion process and residual fraction was submitted to fermentation using an in vitro model of human faeces. For both fractions, high concentrations of ferulic and coumaric acids (peels: 70 mg 100 g-1 and 113 mg 100 g-1, respectively and for stems: 95 mg 100 g-1 and 68 mg 100 g-1, respectively) were detected after the GIT simulation, as well as after 48 h of microbiota fermentation, demonstrating a high antioxidant potential during all stages of GIT. The stem flour promoted in the same extent the growth of Lactobacillus spp. and Bifidobacterium spp., while peel flour promoted mainly the growth of Lactobacillus spp. The growth of such strains led to the production of short chain fatty acids (SCFA), mainly propionic and acetic acids, which positively modulated the gut metabolism. A proof of concept of one of developed ingredients was carried out by the application of bromelain in the process of tenderization in a traditional ham. The lowest bromelain concentration tested (1 mg mL-1) still led to the tenderization of the pork meat. Through an experimental factorial design, the values range and optimum enzyme application conditions were selected: 1 mg of bromelain per mL of brine. The results from this experimental work will certainly contribute for the sustainability of fruit processing industries in a circular economy context through development of value-added ingredients with biological and functional impact. Moreover, the development of six new functional ingredients, through a ZERO waste approach by application of an integrated downstream process will help fruit processing industries to implement low-cost solutions with high value-added final products, which allows the re-integration of economic value, the generation of new revenue streams and encouraging a more sustained society.
Date of Award2019
Original languageEnglish
SupervisorMaria Manuela Pintado (Supervisor) & Lorenzo M. Pastrana (Supervisor)

Designation

  • Doutoramento em Biotecnologia

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