Vol. 12, Issue 6 (2023)

The present research entitled “Thermal imaging and physico-chemical properties based maturity indices for custard apple fruit (Annona squamosa L.)’’ was studied at the ICAR-National Institute of Abiotic Stress Management, Baramati, Dist. Pune during 2021-2022. The objectives of present research were to determine changes in physico-chemical properties of custard apple fruit during maturation and to investigate the utility of thermal imaging for predicting the right harvesting time of custard apple fruit.

Custard apple (Annona squamosa L.) is climacteric, deciduous and subtropical fruit cropcommercially cultivated because of its hardy nature for abiotic and biotic stresses. After genotype, maturity stage at harvest is second most important influencing factor of fruit quality which depends on physicochemical properties at harvest. Objective type maturity indices determined by precise instruments are reliable and commercially applicable for fruits like custard apple where determination of right maturity level is critical. For this purpose the research was carried out to study the changes in physico-chemical and thermal characteristics of custard apple fruit during ripening. Considering the fact of heat release due to respiration the experiment of studying the temperature changes in custard apple fruit during ripening was carried out. Firstly harvesting of custard apple fruits according to aeroles opening levels namely A0, A10, A25, A50, A75, A100 meaning 0%, 10%, 25%, 50%, 75%, 100% of aeroles opening during maturation. Harvested fruits of each stage were sampled after every 3 days of storage to determine changes in fruit surface temperature and physicochemical properties. Correlations between different properties of custard apple fruit is expressed using Pearson’s correlation matrix. Based on the correlation between physico-chemical and thermal properties collective, reliable, nondestructive maturity indices for custard apple fruit is provided.

The quality attributes of custard apple fruits (Cv. Balanagar) at harvest of A0, A10, A25, A50, A75 andA100 includes true density (g/cc) of 0.96±0.01, 0.97±0.01, 0.99±0.01, 1.04±0.01, 1.08±0.01, 1.10±0.01; penetration force (g) of 2204.6±52.1, 2165.7±55.4, 2062.6±49.0, 1819.3±63.2,1517.8±49.9, 1352.6±54.0; cutting force (g) of 19882.9±671.8, 18574.5±453.0, 17163.9±883.9, 14591.8±342.9, 11615.9±401.5, 9633.5±445.1; pulp/seed ratio of3.2±0.2, 3.8±0.3, 5.3±0.4, 7.0±0.4, 7.7±0.3, 8.1±0.2;total soluble solids (°B) of 10.5±0.9, 11.0±0.9, 11.9±0.3, 12.9±0.3, 14.4±0.5, 16.2±0.9; total sugar (%)of 6.8±0.9, 7.8±0.4, 8.8±0.6, 11.0±0.5, 12.9±0.6, 15.2±0.6; titratable acidity (%) of 0.31±0.01, 0.30±0.01, 0.29±0.01, 0.26±0.01, 0.23±0.01, 0.21±0.01; moisture content (%) of 64.2±0.4, 64.8±0.4, 66.2±0.6, 68.4±0.6, 71.4±0.6, 72.6±0.5; fruit surface temp. (°C) of 27.8±0.1, 28.0±0.2, 28.1±0.2, 28.7±0.3, 29.1±0.1, 29.4±0.2 respectively.

The custard apple fruits of all stages were stored under laboratory condition (22-28 °C). The different maturity stages at harvest significantly influence the physico-chemicals as well as thermal parameters of fruits. The fruits were analysed at the interval of three days by measuring the physiological weight loss, true density, penetration & cutting force, pulp/seed ratio, total soluble solids, titratable acidity, moisture content and fruit surface temperature. It is found that the physiological weight loss continuously increases throughout the entire storage period.True density increases cumulatively thereafter declines across all aeroles opening levels during storage. The cutting and penetration forces are continuously decreases throughout the storage period. Also the pulp/seed ratio increases and then declines. Total soluble solids, total sugar and moisture content increased in the early stage of storage and then decreased. The titratable acidity declines continuously throughout entire storage period. Fruit surface temperature increases and reaches its peak during ripening followed by decline at end of storage.

The experiments showed that fruits of A0, A10, A25 are of poor quality with lower fruit surface temperature while fruits of A50, A75, A100 having better fruit quality attributes with higher fruit surface temperature. The custard apple fruits with aeroles opening level A50 was found to be the best based on physico-chemical, thermal and correlation data.