Evaluation of a Non-Destructive Dry Matter Sensor for Kiwifruit

In this work we studied the relationship between kiwifruit dry matter (DW) measured using the destructive method with a fruit dehydrator (Nesco/American Harvest®, Wisconsin, USA) and a non-destructive Kiwi meter sensor (Turoni Inc., Forli, Italy). This was an approach to develop a reliable non-destructive method to predict harvest and postharvest quality based on dry matter. There was a significant, but low correlation between DM determined non-destructively using the Kiwi meter and destructively using the fruit dehydrator (industry standard). Classification models with discriminant analysis were used to segregate kiwifruit into groups according to DM. Using this statistical approach rather than the relationship between the two methods, kiwifruit were consistently segregated into two DM groups, but classification into three groups yielded lower scores. These results indicate that the Kiwi meter is a reliable and fast sensor to segregate kiwifruit according to their DM content that could be considered as a consumer quality at harvest and/or postharvest index. Further work on the optimization of this non-destructive sensor as a tool to define consumer kiwifruit quality is being carried out by our group. INTRODUCTION Currently, kiwifruit is marketed worldwide. This globalization has created economic advantages for early and late harvest kiwifruit sales, when commodity availability is low and prices are high. This situation has created an incentive for early harvest, which can result in low consumer-quality kiwifruit in the market, reducing repeat purchases of kiwifruit and overall demand (Woodward and Clearwater, 2008). Therefore, a more reliable, fast, and simple quality index that assures taste quality, protecting consumers, is needed. Because dry matter (DM) includes starch concentration, and is highly correlated with ripe SSC and final soluble sugars after ripening (Harker et al., 2009; Hopkirk et al., 1986; Jordan et al., 2000), researchers from various countries have proposed the use of DM concentration as a quality index. As a result, some industries have started its use for trading. Non-destructive sensor methods, such as near infrared spectroscopic (NIR) analysis or density, can be used to assess kiwifruits in terms of their dry matter content and/or ripened soluble solids content (SSC) (Crisosto et al., 2009; McGlone et al., 2002; Moghimi et al., 2010; Nicolai et al., 2007). The commercial motivation underlying these methods is the desire for fast grading, according to optimum, consumer-defined quality. The taste of ripe ready-to-eat kiwifruit is largely determined by the fruit SSC, and this final SSC is highly correlated with the DM of unripe fruit. The research objective of this study was to assess the accuracy of the Kiwi meter non-destructive sensor to determine kiwifruit quality, compared with destructive, traditional methods. The main goal of this study is the non-destructive prediction of the DM of kiwifruit, in order to provide a fast and non-destructive parameter to decide the correct time of harvest based on consumer acceptance. MATERIALS AND METHODS For this study, kiwifruits (‘Hayward’) were evaluated for destructive and nondestructive dry matter content. Fruit was harvested from experimental and commercial fields in California and Chile at its commercial maturity. Fruit was transported to UC