Ripening tomato fruit after chilling storage alters protein turnover

Tomato fruit is of prime importance owing to its qualities for human nutrition and its economic value. In order to extend its commercial life, it is harvested at mature but unripe stages and stored at low temperatures. The goal of this work was to study the influence of harvest and chilling storage of mature green tomato fruit (cv. Micro-Tom) on the protein pattern, amino acid content and protease activity during fruit ripening.

Fruits were sampled during ripening in three different conditions: 1, on the vine; 2, off the vine; 3, off the vine after 4 weeks at 4 °C. During all fruit ripening conditions, protein level decreased while amino acid content increased. Chilling storage of mature green fruit led to a reduction in protein content. Ripening off the vine (conditions 2 and 3) resulted in a threefold increase in red fruit amino acid levels when compared with red fruit on the vine. Protease activities (autoproteolytic, azocaseinolytic and gelatinolytic) were detected in all fruits evaluated and were differently affected by ripening stage, ripening conditions and the presence of specific inhibitors.

Harvest and chilling storage increased endogenous substrate proteolysis, azocaseinolytic activity and free amino acid levels, which could be related to fruit quality.