ISHS Acta Horticulturae 464: International Postharvest Science Conference Postharvest 96
TEXTURE AND QUALITY OF PLUMS IN RELATION TO DEGREE OF RIPENESS AND STORAGE CONDITIONS |
| Authors: | W. Plocharski, D. Konopacka |
| Abstract:
In these experiments, fruit of three cultivars picked in the 1995 season were used: ‘Dabrowicka Prune’, ‘Prune No 589007’ and ‘Valievka’. Fruit were stored at room temperature or at 0°C for 10 d, then for an additional few days at room temperature. On the picking day and after storage, fruit were tested for quality indices related to ripeness (L*, a*, and b* values of fruit flesh, acidity and soluble solids). Firmness of fruit was also checked with a nondestructive method based on measurement of apparent modulus of elasticity, using an Instron (Model 4303). Organoleptic tests were made on fruit either immediately after picking or following storage, using a computerized system of data collection. The experiments are mainly concerned with the methodology. The results obtained showed that the nondestructive method of measuring plum texture, based on testing of apparent modulus of elasticity, is promising. There was an almost perfect correlation (r = 0.998) between load and displacement within the range of 0.25 – 1.00 N. The method allowed better discrimination between different classes of fruit ripeness than other standard parameters, including soluble solids content, soluble solids/acids ratio, and Hunter L*a*b* values or a*/b* ratio for fruit flesh. Using this method, fruit of the three cultivars were separated into different elasticity classes. There was a high correlation (R2 > 0.8) between coefficient of elasticity and degree of ripeness as estimated by the organoleptic method. Results obtained suggested that the preference for ripeness expressed as apparent modulus of elasticity depended on cultivar. Preliminary data showed that ‘Prune No 589007’ was more acceptable when the modulus of elasticity was about 0.14 MPa, whereas for ‘Valievka’ the value was 0.19 MPa. This difference may be partly related to the soluble solids to acids ratio, which was lower in ‘Prune No 589007’ than in ‘Valievka’. For the cultivars tested there was significant correlation (better than 0.7) between modulus of elasticity and soluble solids content in fruit. Evidently, modulus of elasticity depends greatly on the turgor of the fruit cells. Fruit stored in sucrose syrup lost 17.2 – 18.7% of its weight (compared to 2 – 2.5% with those stored in air), and the values of modulus of elasticity fell dramatically. During storage of the fruit at room temperature, the coefficient of elasticity values decreased at a different rate in relation to the initial degree of ripeness. Fruit picked unripe underwent more rapid changes than fruit picked at more advanced maturity. The quality of fruit picked at full maturity decreased greatly during storage and they were rated significantly lower than fruit picked earlier. The results suggest that fruit intended for storage should be picked slightly earlier than for direct consumption. In summary, the nondestructive method for measuring apparent modulus of elasticity may be successfully used for estimating picking maturity of prunes and for checking uniformity of ripening in relation to cultivar. Modulus of elasticity of prunes correlates well with some other fruit quality indices (soluble solids, organoleptic tests) and may be used for prediction of fruit quality during storage. There was an association between modulus of elasticity of fruit after picking and the rate of softening during storage - unripe fruit underwent faster changes than the ripe ones. Results show that fruit intended for storage should be picked at a firm ripe stage of development (modulus of elasticity higher than 0.2MPa). | |
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