For many years, type II diabetes with a characteristic of postprandial hyperglycemia has been a public health concern worldwide. A fast conversion of starch to glucose through starch digestion is considered one of the primary causes of postprandial hyperglycemia [1]. Therefore, many strategies such as chemical, genetic and physical modification have been applied to slow the digestion rate of starch. Among them, physical modification has attracted more and more attention due to its high acceptability from consumers. One of physical modification methods is to increase slowly digestible starch (SDS) and resistant starch (RS) fractions in starch foods by adding edible compounds such as polyphenols or their extracts [2]. This brings light to potential application of polyphenol in development of starch-based functional food products with lower digestion rate and extent.

Numerous researches reported that polyphenol showed important functions of controlling starch digestion and decreasing postprandial blood glucose levels [3,4]. In terms of boosting the fractions of SDS and RS in starch foods, polyphenol could interact with starch and changed the physicochemical characteristics of starch to impede the digestive process and thus lowered the post prandialglucose level [5,6]. The interaction between polyphenol and starch was primarily driven by non-covalent force including hydrogen bonding, van der Waals force, and hydrophobic interaction [7]. On the molecular level, the interaction between polyphenol and starch could result in two types of complexes: V-type inclusion complex and non-inclusion complex [8]. Starch-polyphenol V-type complexes were considered as type 5 RS [9]. Type of starch-polyphenol complex was related to composition and structure of polyphenols [10], the ratio of amylose to amylopectin [11,12], etc. Unfortunately, the possible mechanism of interaction between polyphenol and starch has not been fully illustrated, and it remains unclear how polyphenol affect the physicochemical characteristics of starch because there are too many polyphenols with different composition and structure and individual polyphenol may synergistically affect the interaction. Therefore, it is meaningful to continue investigating the specific mechanism of starch-polyphenol interaction and the impact on starch digestibility.

Persimmon (Diospyros kaki L.) is widely cultivated for a long time in Asia, including China, Japan, and Korea. Persimmon leaf (PL) is a traditional Chinese herb medicine and is also well-known as functional tea [13]. It was reported that PL contained polyphenols and had a range of physiological actions, including anti-inflammatory, immunomodulatory, and digestive enzyme inhibitory properties [[14], [15], [16]]. However, to our knowledge, very limited research can be found regarding the interaction between persimmon leaf polyphenol (PLP) and starch and the effect on starch digestion.

In present study, the interaction between corn starch with varying amylose contents and PLP was investigated, along with the effect of the interaction on starch digestibility and antioxidant activity. The interaction was studied by using a variety of techniques, including UV-absorption spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, Thermogravimetry, Differential scanning calorimetry, and Nuclear Magnetic Resonance. The results of this study would not only provide a theoretical basis for targeted regulation of starch digestibility but also be beneficial for the comprehensive utilization of PL.