Pumpkin, belonging to the Cucurbitaceae family, is extensively cultivated in temperate and subtropical regions of the world, with a global production of 23.78 million tons [1]. Pumpkin seeds, a by-product of pumpkins, are a nutritious dietary source for humans due to their high content of linoleic and oleic acids, which make up approximately 75 % of the total fatty acids [2]. However, due to high levels of unsaturated fatty acids, pumpkin seeds are susceptible to be oxidized, leading to the production of small molecule compounds such as aldehydes, ketones, and acids, which generate strong irritating odor (hallucinogenic) [3]. Currently, synthetic antioxidants, such as tertiary butyl hydroquinone (TBHQ), propyl gallate (PG), and butylated hydroxyanisole (BHA), remain the primary antioxidant to prevent oxidation reactions in pumpkin seeds. But the synthetic phenolic antioxidants and their metabolites pose a threat to human health because they could cause DNA damage, carcinogenicity, and apoptosis [4]. Consequently, there has been a substantial surge in interest in the quest for alternative antioxidants derived from natural sources.

Anthocyanins, a recognized natural antioxidant, are ubiquitous in grains, fruits, and flowers, such as black rice, blueberry, roselle, and purple potato [5]. They could directly eliminate reactive oxygen species (ROS), protect cells from oxidative stress and inactivate lipoxygenase, and their potential roles in capacities of scavenging peroxyl radicals and activities of cellular antioxidant in vitro were extensively evaluated [[6], [7], [8]]. Black rice (Oryza sativa L.), a special kind of rice, appears black and purple color due to the thick deposition of pigments like anthocyanins in the pericarp layer. It is widely cultivated in China, Japan, Thailand, and other East Asian countries [9]. In previous study, cyanidin-3-glucoside (C3G) was determined the major component of anthocyanin in black rice, accounting for about 85 % [10,11]. Specially, Yazdankhah et al. [12] found that the antioxidant activity of black mulberry extract was stronger than TBHQ and vitamin C, attributed to the presence of cyanidin-3-glucoside (C3G).

Cyanidin-3-glucoside was made of the basic structure, 2-phenylbenzopyran cation, which is hydroxylated at various positions (C3, C5, and C7) and mainly glycosylated at C3 [5]. The chemical structure of anthocyanins is strongly hydrophilic and weakly oleophilic, rendering them sensitive to various environmental conditions, including pH, light, temperature, and oxygen, which leads to structural destruction, color fading, and decreased antioxidant activity [13,14]. Due to the low stability of anthocyanins, direct addition to pumpkin seeds is not a feasible option. In order to preserve the stability and bioavailability of anthocyanins, several methods such as acylation [11], co-pigmentation [15], and embedding with edible biological film [16,17] have been studied and applied. Among them, embedding with edible biological film is a practicable and effective technology, for its cheapness, convenience, and scale ability, which could be able to combine anthocyanins through hydrogen bonds to produce a film preserving anthocyanins from the external environment. In addition, the film is formed on the surface of the pumpkin seeds by dipping them in film solution and then drying them, which creates a barrier between pumpkin seeds and outside environment to limit oxygen entry, prevent oxidation, and minimize quality deterioration [18]. Priyadarshi et al. [19] developed a pectin/pullulan blend film incorporated with grape seed extract, effectively delaying the oxidation of peanuts.

Over the past decades, starch and its derivatives have been widely preferred biopolymer for the formation of films, attributed to their advantages of low price, abundant reserves, good biodegradability, high biocompatibility, and good film-forming properties [20]. Acetylated cassava starch (ACS) is a starch derivative obtained by the substitution reaction of hydroxyl groups in native cassava starches with acetylating agents [21]. Nevertheless, single starch films have strong hydrophilicity and poor oxygen barrier, limiting their applications. Sodium carboxymethyl cellulose (CMC) is considered as a suitable filler for biological composite films due to the polymeric structure and high molecular weight, and it plays a crucial role in preventing the escape of oxygen and carbon dioxide, as well as improving the mechanical strength of the film [17,22]. The mixture of acetylated cassava starch and sodium carboxymethyl cellulose could overcome the shortcomings of single component. Several researches have performed the film based on anthocyanins and different biopolymers, such as starch/polyvinyl alcohol [23], pectin [16], and chitosan/polyvinyl alcohol [24], but no one has studied the immobilization effect of AEBR in ACS/CMC mixture, the stability of AEBR, and the antioxidant effect of AEBR film on pumpkin seeds during storage.

Therefore, in our study, we aim to embed AEBR into acetylated cassava starch/carboxymethyl-cellulose (ACS/CMC) to enhance the stability of AEBR in application of pumpkin seeds. Different AEBR contents were incorporated into ACS/CMC, and then formed a film as a barrier to prevent oxidation of pumpkin seeds, thereby improving their shelf life. The impact of addition of AEBR to ACS/CMC film on steady, dynamic rheological properties was analyzed. The microstructure and chemical properties of the film were also evaluated. Moreover, the effects of different AEBR additions on mechanical properties, thickness, water vapor transmittance, UV–vis light transmittance, and opacity of the film were comprehensively investigated and compared. Finally, the quality characteristics of pumpkin seeds coated with different AEBR films stored under different conditions and the correlation between anthocyanins and quality parameters (peroxide value, acid value, and color parameters) of the pumpkin seeds were estimated.