Fruit residues: Low cost substrates for development of new food products

Abstract

Juice and beverage industries produce ~125 million tonnes of fruit and vegetables byproducts annually. Within this context, new social and environmental concerns are challenging the current agri-food systems towards more sustainable practices from production to distribution. In this study, fermentation processes to convert fruit and vegetable pomaces into new food products with enriched nutritional and commercial value for human consumption were developed based on a comprehensive chemical characterisation of these by-products. It was critical to build a more comprehensive picture of the compositions of the fruit and vegetable pomaces to determine their potential for value-adding technologies. A wide range of bromatological and mass spectrometrybased metabolomic analyses were used to chemically characterise apple, orange and carrot pomaces, demonstrating that each of the pomaces has a chemical composition even more diverse than has been previously described. In addition, untargeted metabolomic tools showed great potential in providing more comprehensive chemical compositions of foods, as well as potentially being useful tools in food safety. More importantly, these data provided insight into the greater potential for bioconversion of these pomaces into highly nutritious and value-added products. Based on the by-products characterisations we selected three groups of food-grade microorganisms to carry out the fermentations: the basidiomycete fungus Pleurotus pulmonarius, the non-Saccharomyces yeast Brettanomyces bruxellensis and a New Zealand isolate of Aspergillus niger and Aspergillus. P. pulmonarius was used to ferment the three pomaces, and during growth, the fungus consumed free sugars and degraded plant polymers converting them into biomass rich in proteins, fungal polysaccharides, and fungal-derived fatty acids, as well as increasing the mineral concentrations and the pH of the fermented pomaces. This fermentation resulted in a low calorie/low-sugar flour, which was also low in fat and high in protein and dietary fibre and can be scaled-up to produce a promising fermented novel food product. I also compared solid and submerged-state fermentation of the three pomaces using B. bruxellensis, non-conventional yeast, to assess its ability to improve the nutritional value of the pomaces. Although there is the possibility of improvement, overall, the fermentation enhanced the nutritional profile of the pomaces by decreasing the concentration of simple sugars and increasing the concentration of dietary fibre, protein, unsaturated fatty acids and minerals content, as well as breaking down the small amount of lignin, which could help to enhance the palatability of these pomaces. Finally, New Zealand isolates of A. niger and A.s oryzae were used to convert fruit and vegetable pomaces into different addedvalue food products/ingredients within a biorefinery approach by producing, concentrating and/or solubilising added-value molecules such as: phenolic acids, oxalic acid, free amino acids, minerals, lignin and dietary fibres. These preliminary results could be substantially improved by optimising a few of the fermentation parameters, which can now be better selected based on the untargeted metabolomics results.