Polymeric proanthocyanidins (PA) interact with starch forming complexes that restrict starch digestibility (Amoako & Awika, 2016a), and may thus lead to new ingredients with nutritionally beneficial effects. The PA interact with starch primarily through non-covalent hydrogen bonding and hydrophobic interactions. In gelatinized starch, hydrogen bonding is dominant, while hydrophobic interactions primarily stabilize starch-PA complexes in intact or minimally gelatinized starch granule (Amoako & Awika, 2019). Under food processing conditions, the non-covalent interactions may be disrupted due to the presence of proteins, lipids, moisture, and heat, negating the potential nutritional benefits of starch-PA complexes. For example, our work recently demonstrated that, although starch-PA complexes were stable during hydrothermal processing in low moisture product (cracker), retaining most of the resistant starch (RS), the complexes were disassembled in presence of gluten proteins in a high moisture system (pancake), losing RS properties (Althawab et al., 2023). The disassembly was attributed to the higher affinity of the gluten proteins than starch for the PA, likely facilitated via hydrophobic attraction between the open-structured glutenins with the PA aromatic rings (Girard et al., 2018). The structural instability of the starch-PA complexes limits their potential use in functional food formulations aimed at health-beneficial applications, such as increasing RS and moderating glycemic response. Strategies to strengthen the starch-PA complex stability is important to develop novel starch-based ingredients that exploit naturally derived bioactive polyphenols to deliver reduced caloric and glycemic impact in foods.

Subjecting starch to ionizing radiation from sources such as gamma and electron beam (Ebeam) can induce molecular changes resulting in starch modification. The ionizing radiation results in the formation of radiolytic free radical products (such as OH• and H•), with capacity to induce molecular modifications and fragmentation of starch polymer (Bashir & Aggarwal, 2019; Bhat & Karim, 2009). The intensity of free radical generation will affect the fundamental characteristics of starch (Sokhey & Hanna, 1993), including its physicochemical properties, as well as its level of digestibility, through degradation and/or crosslinking reactions. The outcomes of starch irradiation are dependent on several factors, including starch botanical source, ionizing radiation source and dosage, and moisture content (Bashir & Aggarwal, 2019; Bhat & Karim, 2009). Such variables can thus be manipulated to facilitate starch-PA interactions and produce starches with desired physico-chemical properties.

Starch is commonly crosslinked with various multifunctional agents (such as phosphorous oxychloride or sodium hypochlorite) with variable outcomes (Shah et al., 2016). The mechanism is believed to involve reaction of the primary (6-OH) and secondary (2-OH and 3-OH) glucose alcohols with the multifunctional reagents resulting in crosslinked starch via either ether or ester inter-molecular bridges. Such crosslinked starch has variable outcomes such as less swelling, and more resistance to shear, temperature and low pH compared to unmodified starch (Koo et al., 2010). However, consumer concerns and labelling requirements restrict the widespread use of chemical crosslinking to enhance resistant starch content in foods (Hagenimana & Ding, 2023). Facilitating covalent starch crosslinking using naturally derived molecules could enhance the appeal of such starches for diverse applications.

Irradiation has been documented to link starch with non-starch polymers such as grafting amylose polymers on polyvinyl alcohol (PVA) to form stable hydrogels (Zhai et al., 2002). The PA have multiple reactive sites in close proximity due to abundant –OH groups (Amoako & Awika, 2016b), and are likely to readily participate in electron transfer reactions under Ebeam energy, facilitating starch crosslinking. Thus, we hypothesize that irradiation process and resulting free radicals will induce covalent linkages between starch molecules mediated by PA, improving starch-PA complex stability to amylase enzyme hydrolysis. The study aimed to investigate the effect of Ebeam on starch-PA complex physiochemical properties and in vitro digestibility.