Development of a novel time–temperature integrator/indicator (TTI) based on the maillard reaction for visual monitoring of melon (Cucumis melo L.) maturity during cultivation

Abstract

Accumulated temperature, representing the sum of average daily temperatures, is an objective index for assessment of the maturity of vegetable and fruit crops, including melon. We attempted to manage melon cultivation using time–temperature indicators (TTIs), that reflect temperature history during the cultivation period. The objective of this study was to develop a method for simple prediction and estimation of melon maturity using TTIs based on the Maillard reaction to assist in the decision of when to harvest melons. We examined the performance of TTIs during melon cultivation in greenhouses. Prototype TTIs were prepared using a combination of d-xylose (1.0–2.0 mol/kg) and glycine (2.0–3.5 mol/kg) and the correspondence between changes in color and time–temperature histories of melons during cultivation investigated. The color of TTIs changed from colorless to dark brown, as expected. In some areas of the greenhouse, accumulated temperatures differed by more than 50 °C day, depending on location within the greenhouse, resulting in variation in the color development of TTIs. TTIs could successfully indicate differences in accumulated temperatures, due to temperature irregularities in a greenhouse, as a difference in color. Furthermore, the relationship between accumulated temperature and melon quality at harvest time was investigated. Accumulated temperature was positively correlated with soluble solids content (SSC) and negatively correlated with melon firmness. The prototype TTIs corresponded well with the level of melon maturity, and can indicate SSC and firmness by color development; therefore, they have potential for use in prediction of individual melon maturity during cultivation.