Pre-processing Waste Tomatoes into Separated Streams with the Intention of Recovering Protein: Towards an Integrated Fruit and Vegetable Biorefinery Approach to Waste Minimization

Abstract

Abstract Purpose A large proportion of the European Union’s tomato crop is discarded during harvesting and there is a valorisation potential to recover proteins from this waste. Methods Cherry tomatoes were segregated into three separate components: juice, pomace (peels and skins), and seeds. The peels and skins, and seeds were separately hydrolyzed with carbohydrases to determine whether protein recovery could be increased. In addition, a strategy to fractionate the seeds was developed using sequential washing of milled tomato seeds, followed by low-speed centrifugation to remove the denser seed hulls and to collect the protein rich kernels remaining in suspension. Results The protein content of the seeds was highest with 27.4% while the peels and skins contained 7.6%. Carbohydrase mediated hydrolysis resulted in a minor increase in protein recovery of 10% from seeds using Filta 02L (cellulase, xylanase and β-glucanase), and the quantity of protein recovered from peels and skins increased by 210% using Tail 157 (pectinase, hemicellulase). The strategy to separate the seeds into two fractions, revealed that a higher proportion of the fibre (65%) was associated with the hull fraction compared with the original seeds (47%). A significant proportion of the fibre in this fraction was composed of lignin although the protein contents between both fractions was similar ranging from 27.4 to 29.9%. Conclusions These results reveal that carbohydrases were quite effective in protein extraction from peels and skins, but not from seeds. An alternative strategy was developed to remove the seed hulls from the milled seeds and to collect a fraction containing protein and dietary fibre where oil could be removed at this stage. Graphical Abstract