Accurate identification of fruit harvest timing is quite a complicated issue. We know several methods of determining harvest maturity in climacteric fruits; these include measurement of: firmness, total solids contents, respiration rate, ethylene emission measurement as well starch tests. On the other hand non-climacteric fruits (no collective maturity phase) are identified as suitable for harvesting by evaluating their colour. The first three aforementioned basic methods can be combined into a single tool, the so-called Streiff index. All the characteristics identified herein, i.e.: starch assay, total solids (including sugars, tannins, vitamins, organic acids, etc.), as well as firmness, corresponding to protopectin-pectin conversion, produce caloric response. Hence, the correlation between fruit maturity and the caloric response of the material provides the basis for an innovative test enabling assessment of harvest maturity in fruit. Caloric response is largely impacted by the changing structure of fruit dry mass. The calorific content of fruit during maturation process decreases due to the conversion of the water-insoluble starch, with a calorific value of 4200 cal/g, into soluble monosaccharides 3750 cal / g. The study presents a novel calorimetric method of assessing harvest maturity in fruit and the presentation is based on fruit of selected varieties of apples, tomatoes and strawberries. The calorimetric maturity thresholds have been determined for these fruits at the following levels: apples – 3930 cal/g s.m., strawberries – 3880 cal/g s.m. and tomatoes - 3910 cal/g.
fruits, harvesting maturity, calorific value