Coatings with the food aditive sodium benzoate, promising to control sour rot on mandarins

Starch is a biodegradable polymeric carbohydrate that can easily form films and coatings and can readily be obtained from some food industry by-products and wastes, which may contribute to the circular bioeconomy. In this work, we studied the potential of two edible coating emulsions based on pregelatinized potato starch (PPS) and glyceryl monostearate (GMS) alone (F6 and F10) or formulated with the food additive sodium benzoate (SB, 2%) (F6/SB and F10/SB) to control sour rot, an important citrus postharvest disease caused by the fungus Geotrichum citri-aurantii, and maintain postharvest quality of cold-stored ?Orri? mandarins. The PPS-GMS coating application was compared to dipping in water (uncoated controls) and dipping in a 2% SB (w/v) aqueous solution. The results showed that the coating F10/SB was the most promising treatment to control sour rot on mandarins, with reductions in disease incidence with respect to the uncoated control samples of 94, 69, and 55% after 2, 4, and 6 weeks of storage at 5 ?C, respectively. Coatings formulated without SB were ineffective. Regarding fruit quality, the coating F10 was the most effective to reduce weight loss, maintain firmness, and provide gloss on mandarins stored at 5 ?C for up to 6 weeks followed by a shelf-life period of 1 week at 20 ?C. The addition of SB to the PPS-GMS coatings adversely affected these coating properties, but the coating F10/SB still reduced weight loss compared to uncoated controls without negatively affecting the fruit physicochemical (juice titratable acidity, soluble solids content, and volatiles content) and sensory quality (overall flavor, off-flavors, external aspect). Overall, the coating F10/SB showed the greatest potential for commercial use as an efficient and environmentally friendly alternative to conventional fungicides and waxes for sour rot control and quality preservation of cold-stored mandarins. ? The text before is the Abstract of the paper. 1. IntroductionCitrus sour rot, caused by the pathogenic fungus Geotrichum citri-aurantii, is an important postharvest disease that has become a major concern in many citrus producing and exporting countries worldwide [1]. The incidence and consequent economic importance of sour rot has increased in recent years, especially in citrus regions with a Mediterranean-type climate, due to the increment of extreme weather events, such as violent rainfalls with large drops, hail, and gusts of intense wind that cause splashes, blows, and rind wounds in the fruits [2,3]. Inoculum of G. citri-aurantii is present in soil particles in citrus orchards and reaches the fruits, particularly those in the lower part of the tree, via water splash during the mentioned weather episodes, especially heavy rains. Once located on the surface of mature fruits, arthrospores of the fungus can invade the rind of the fruit through injuries and bruises, especially deep wounds that extend into the albedo. Successful infections on immature fruits or through shallow rind injuries are more difficult to occur [1,2]. Sour rot lesions on citrus fruits are watery, soft, and of glutinous nature, and under high relative humidity (RH) a yeasty, wrinkled layer of whitish mycelium is formed on their surface. Infected tissues have a characteristic yeasty, vinegary odor that attracts fruit flies and other insects that may also contribute to disease dispersion [1]. Treatments with conventional chemical fungicides, such as imazalil, fludioxonil, pyrimethanil, o-phenyl phenol, and sodium o-phenyl phenate, serve as the primary means to commercially control postharvest diseases of citrus fruits [1,4]. However, these agrochemicals are devoted to the control of Penicillium molds, which are generally the most important citrus postharvest diseases causing economical losses, and they do not control sour rot effectively [5]. Guazatine and propiconazole are fungicides with proven, high effectiveness against G. citri-aurantii, but they have been withdrawn from the market in the European Union (EU) because of their high toxicity to humans and the environment. Therefore, the lack of authorized fungicidal active ingredients for sour rot control in the EU and other citrus producing areas is a serious threat for the marketing of high-quality citrus fruits, and there is an increasing need for safe and effective nonpolluting alternative strategies to control citrus postharvest sour rot [6,7]. The use of some common salts classified as generally recognized as safe (GRAS) compounds or food additives is a promising eco-friendly alternative to synthetic fungicides for citrus sour rot management [6,8]. Recently, a study conducted by our group showed that dipping fruit in aqueous solutions of sodium benzoate (SB) at 3% (w/v) for 60 s at 20 or 50 ?C has a strong curative effect, similar to that of the chemical fungicide propiconazole, against sour rot on mandarins and oranges artificially inoculated with G. citri-aurantii [7]. In addition, Smilanick et al. [9] reported that immersion of inoculated lemons in 1% (w/v) sodium bicarbonate solutions for 1 min at 24 ?C reduced the number of viable spores of the pathogen. Sour rot incidence was also reduced moderately after treatment with a potassium sorbate solution at 1% (w/v) for 30 s at 50 ?C on lemons inoculated with G. citri-aurantii 24 h before treatment [10]. Furthermore, sodium salicylate, boric acid, EDTA, sodium dehydroacetate, and sodium silicate also exhibited significant potential for sour rot control on mandarin fruit [11,12]. However, some of these aqueous treatments lacked persistence and/or adversely affected the quality attributes of treated fruit. Postharvest use of composite edible coatings (ECs) based on food grade, biodegradable materials is a promising approach to maintain postharvest quality and extend the life of fresh horticultural produce, particularly fresh fruits and perishable fruit vegetables [13,14]. Starch-based coating matrixes can be used for this purpose due to their compatibility with a wide range of functional compounds, relative low cost, and desirable film characteristics. Furthermore, starch is a biodegradable polymeric carbohydrate that can be easily obtained from different sources, including food industry by-products and wastes, which can contribute to the circular bioeconomy. In general, starch films are odorless, transparent, taste-free, non-toxic, and highly impervious to O2. However, typically, starch films have high water vapor permeability and additional ingredients are needed in the emulsion to obtain coating matrixes suitable to reduce water loss, and consequently, weight loss, during long-term storage of horticultural produce. Hence, the addition of hydrophobic compounds such as lipids and other minor ingredients such as plasticizers and emulsifiers is reported to improve the properties of starch-based films [15]. Thus, composite starch matrixes formulated with appropriate lipidic materials and other adjuvants have successfully modified the gas composition within the fruit and reduced weight loss through the regulation of gaseous exchange (O2, CO2, and water vapor) between coated fruits and vegetables and the ambient atmosphere [16]. An important advantage of ECs is the possibility of incorporating food additives or GRAS salts as additional ingredients into the basic coating formulation [14]. Nevertheless, the addition of these additional functional ingredients to coating matrixes can lead to the formation of unstable or incompatible emulsions showing phase separation, modify the functional properties of the coating, and/or change the organoleptic profile of the coated product. In some cases, the additional ingredient can even lose their functionality when reacting with some original coating components [13]. There is, therefore, a general need to develop tailored EC emulsions for each particular purpose and fresh commodity [14,17]. Available information in the literature on starch-based films formulated with antimicrobial agents is limited. Mar?n et al. [18] found that corn starch-based coatings applied as carriers of the antagonistic yeast Candida sake reduced the incidence of postharvest disease caused by Botrytis cinerea on coated grapes. Likewise, potato starch coatings containing Lactobacillus plantae also reduced grape gray mold. The addition of natamycin/methyl-?-cyclodextrin complex to corn starch ECs reduced weight loss, delayed ripening, and inhibited gray mold on cherry tomato fruits during storage at 22 ?C [19]. Moreover, different thyme essential oils amended to starch?gellan films showed high antifungal activity in vitro and, furthermore, significantly reduced gray mold caused by B. cinerea and black spot caused by Alternaria alternata on persimmons and apples during incubation at 25 ?C of artificially inoculated and coated fruits [15]. In another research work, the GRAS salt potassium sorbate was better retained when it was incorporated into a starch-based EC formulation, which enhanced its antifungal activity and persistence against spoilage molds on refrigerated apples, tomatoes, and cucumbers [20]. In a previous study, Soto-Mu?oz et al. [21] developed and optimized a formulation for an antifungal composite EC based on pregelatinized potato starch and glyceryl monostearate (PPS-GMS) with the addition of SB as antifungal ingredient. This formulation presented curative activity against postharvest diseases caused by Penicillium digitatum, Penicillium italicum, or G. citri-aurantii on artificially inoculated ?Orri? mandarins coated and incubated at 20 ?C for 7 days. In addition, this formulation also reduced mandarin weight loss without negatively affecting the overall fruit quality and consumer acceptability. Nevertheless, no information is available about the performance of this type of coatings during commercial long-term cold storage of mandarins, and such data are necessary to validate the performance of ECs under practical commercial conditions. Therefore, the objectives of this research work were to: (i) assess the ability of antifungal PPS-GMS ECs formulated without or with SB to reduce the development of sour rot and (ii) determine the effects of EC application on the physicochemical and sensorial quality of ?Orri? mandarins during long-term cold storage at 5 ?C plus shelf life at 20 ?C. SourcesPostharvest Application of Potato Starch Edible Coatings with Sodium Benzoate to Reduce Sour Rot and Preserve Mandarin Fruit QualityLourdes Soto-Mu?oz, Mar?a B. P?rez-Gago, Victoria Mart?nez-Blay & Llu?s PalouCoatings 2023, 13(2), 296; https://doi.org/10.3390/coatings13020296 PictureTanau Agritech Portal, Sour Rot: Galactomyctes citri-aurantii (formally, Geotrichum candidum).https://agritech.tnau.ac.in/crop_protection/crop_postharvest_citrus_4.html