Development of a Non-destructive Starch Concentration Measurement Technique in Saffron (Crocus sativus L.) Corms Using Light Scattering Image Analysis

Abstract

In recent years, the demand for acquiring information from agricultural products as part of quality inspection has greatly increased. In Japan, it is necessary to simultaneously realize high quality and produce high-value-added crops to secure a competitive advantage over foreign products (Cabinet Office, 2019). A plant factory is a food production system that enables the year-round production of crop plants under fully controlled environmental conditions (Takatsuji, 1997). While plant factories have contributed to a continuous supply of high-quality products, they have issues with profitability, which may arise from a lack of added-value. To develop value-added products for plant factories, this study focused on medicinal plants with high market value. Since medicinal plants usually require a long cultivation period and a large amount of labor, farmers have limited interest in cultivating these crops (Furumatsu and Inui, 2013). Furthermore, the quality of medicinal plants is strongly influenced by cultivation methods and the growing environment. Therefore, plant factories are well suited to the cultivation of medicinal plants due to their ability to produce high quality, value-added plants. Saffron is a bulbous, medicinal plant in the genus Crocus of the family Iridaceae, and the stigma is harvested to produce one of the world’s most expensive spices (Shoyama, 2009). Also, saffron is considered a medicinal plant, and it has been registered with the Japanese Pharmacopeia (Gazerani et al., 2013). The main constituents contained in saffron stigmas are red carotenoid pigments, picrocrocin and fragrant safranal (Shoyama, 2009). Moreover, it contains crocin, which has medicinal properties. To increase stigma production and enhance crocin content within a limited cultivation area, selecting corms that produce an abundance of flowers is necessary. At present, corm weight is used as an indicator in selection due to previous reports that corm weight of 20 g is highly correlated to desirable bloom capability (Pharmaceutical Affairs Bureau, 1995). However, corm weight is not a precise indicator since the number of flowers produced varies greatly, even when the weight of corms is the same. Therefore, the development of more accurate and precise selectable traits and techniques is necessary. Corms store a high concentration of carbohydrates needed for flowering (Ohyama et al., 1986). b -carotene, which is the initial material in the biosynthetic pathway of crocin, is composed of glucose (Bolhassani et al., 2014). Because starch is one of the storage forms of glucose, crocin content may be affected by starch content. Given these facts, this study also aimed to test the hypothesis that corm selection based on starch concentration prior to planting would increase the number of flowers harvested as well as the concentration of crocin within the stigma compared to selection by weight alone. Starch granules in plant storage tissues, such as corms, are accumulated within amyloplasts in cells (Chino, 1991), which affects the physical cell structure within a corm. Detecting this accumulation is difficult using nearinfrared spectroscopy to measure physical properties,