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Temperature sums experienced before harvest partially determine the post‐maturation juicing quality of oranges grown in the Murrumbidgee Irrigation Areas (MIA) of New South Wales
Author(s) -
Hutton Ronald J,
Landsberg Joseph J
Publication year - 2000
Publication title -
journal of the science of food and agriculture
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.782
H-Index - 142
eISSN - 1097-0010
pISSN - 0022-5142
DOI - 10.1002/(sici)1097-0010(20000115)80:2<275::aid-jsfa526>3.0.co;2-r
Subject(s) - brix , titratable acid , sweetness , fruit juice , horticulture , citrus fruit , orange juice , postharvest , mathematics , sugar , harvest time , food science , biology
Fruit acid levels are important to maturity standards for both fresh fruit and juice acceptability for processing oranges. Citrus fruit maturity standards are based on sweetness (Brix), titratable acidity (% acid) and their ratio. Harvest of Navel oranges for fresh juice can extend for up to 3 months (August–October) and for as long as 7 months (November–June) for Valencia oranges after they first reach acceptable fresh market maturity. Juice processors encourage ‘late hanging’ of fruit on trees to secure a continuous supply of fresh juice. During this time, gradual changes occur in % acid, Brix and juice content. This study tested the hypothesis that a significant proportion of the variation in fruit quality late in the harvest season could be accounted for by environmental conditions during the period that the fruits were left on the trees. Fruit juice quality was assessed in terms of Brix and % acid at the time of harvest for 19 000 fruit deliveries during a 9 year period from 1988 to 1996. The relationship between quality (Brix and acid content) and temperature sums (effective heat units—EHUs) for the period the fruits were held on the trees was tested. A temperature sum (‘day degree’) model for predicting relative changes in acid and Brix content of late‐harvested fruit was developed for both Valencia and Navel oranges. The juice acid relationship with EHUs was stronger than the Brix relationship with EHUs. In addition, the seasonal ‘behaviour’ of % acid was more consistent than that of Brix in both Valencia and Navel oranges. A linear reduction in % acid with increasing EHUs was evident in both varieties. Estimates of fruit quality (Brix/acid ratio) at harvest time should be made using the equations describing changes in % acid with EHUs and the relationship between Brix and % acid to determine Brix. These equations have potential use in predicting the internal quality of citrus fruit during extended harvest periods. EHU‐based fruit quality estimates could determine harvest schedules that enable growers to achieve the optimum factory price for their fruit whilst maximising returns to processors through more efficient product utilisation. © 2000 Society of Chemical Industry