Evaluation of methods for determining rachis browning in table grapes

- Scanning rachis was confirmed to be a viable approach for measuring rachis browning.
- Rachis auto-fluorescence is a fast and useful measure of browning.
- Rachis browning became a significant problem after 3 days of shelf life.
- Web site was developed to quantify browning of scanned rachis.

Rachis browning is an important quality parameter of table grapes which can limit the development of novel storage technologies. Previous research has shown the feasibility of using image analysis by photography or scanning to measure rachis quality. Here, these two methods were compared, and rachis browning was also evaluated by auto-fluorescence. Two table grape cultivars, Mystery and Superior, were stored under different conditions and durations and the three objective methods were employed, in addition to a subjective evaluation. As shown in the past, weight loss was poorly correlated to rachis browning. Correlation coefficients between image analyses by photography and scanning were 0.88 and 0.98 for 'Mystery' and 'Superior', respectively, suggesting that the two methods are interchangeable. Auto-fluorescence compared to photographic image analysis yielded correlation coefficients of 0.73 and 0.90 for 'Mystery', which had a low range of browning, and 'Superior' which had a wide range of browning, respectively. For 'Superior' the lower median of browning had a low correlation to auto-fluorescence whereas the high median range was highly correlated. In general, all methodologies asserted that 3 d of shelf life is a feasible time frame for both cultivars under the conditions tested. A web-based application http://www.agri.gov.il/en/blogs/chapter.aspx?peopleId=21&chapterId=472 was established to upload images and retrieve rachis-browning data.