Soursop (Annona muricata L.) is a tropical fruit rich in polyphenols and antioxidants but with a short postharvest life prone to browning and reaching senescence after 5 d at room temperature (Vu et al. 2023). Soursop fruits approaching senescence during storage have greater softness and deteriorated levels of vitamin C, polyphenols, and total soluble solids (Vu et al. 2023). Preserving nutritional and sensory qualities of soursop is important in preparing it for commercialization.

Edible coatings are composed of edible polymers that protect fruit from the external environment (Kumar et al. 2017). They create a semipermeable protective layer around the fruit surface that modifies the surrounding gaseous environment (Yadav et al. 2023). This reduces respiration rate and ethylene biosynthesis, which extends shelf life (Kumar et al. 2017). Different polymers may have varying levels of effectiveness depending on the physical qualities of the tropical fruit on which they are applied (Yadav et al. 2023).

The present study explored the use of a lipid ester edible coating to preserve soursop. Nature-Cote AVO edible coating is a water-soluble polymer composed of food-grade monoglycerides, diglycerides, and sorbitan esters. The untreated control and the coated fruit were compared over 7 d for total soluble solids (TSS), titratable acidity (TA), total phenolic content (TPC), total antioxidant capacity (TAC), and volatiles.

Materials and Methods

Fruit with 14.8 °Brix and 0.52% TA were picked from a farm in Keaau, HI, USA. Nature-Cote AVO was obtained from JBT Corporation (Chicago, IL, USA). Five milliliters of coating solution was brushed onto the fruit surface and air dried. The control and coated fruit were stored for 7 d at a temperature of 20 ± 0.5 °C with a relative humidity of 45%. Three samples each were taken for control and coating treatments, and the experiments were conducted in triplicate. Fruit pulp was taken from both hemispheres of the fruit. The juice was strained with cheesecloth. The TSS of the juice was measured with a PAL-3 Atago refractometer (Bellevue, WA, USA). The TA of the juice was measured with the GMK-835N acidity meter (G-WON, Seoul, South Korea), and the result was expressed as percentage.

The TAC was determined with the TAC kit (MAK334, ThermoFischer, Pittsburgh, PA, USA). Absorbances were measured at 570 nm using a SpectraMax M2 (Molecular Devices, Sunnyvale, CA, USA). The Folin-Ciocalteu method was used to determine the TPC (Spanos and Wrolstad 1990). Absorbances were measured at 750 nm using the SpectraMax M2.

Volatiles were examined using solid-phase microextraction-gas chromatography mass spectrometry using a divinylbenzene/carboxen/polydimethylsiloxane fiber following an adjusted method seen in prior studies (Li et al. 2020). Samples were extracted as described in a previous study (Yusufali et al. 2024). The adjusted oven temperature regime was: 40 °C (5 min), 15 °C·min⁻¹ to 250 °C, and 5 min at 250 °C. Compounds were identified by their linear retention indices and structure.

One-way analysis of variance with a P value threshold of 0.05 was used to assess changes in the organoleptic qualities of soursop fruit induced using edible coating.

Results and Discussion

The TSS/TA ratio of the coated fruit was 13% higher than control (Table 1). There were no negative effects on fruit quality in the coated fruit as indicated by the TSS/TA values. The TA in coated fruit was significantly lower than the control (Table 1), which may reflect increased organic acid breakdown by the coating treatment (Batista-Silva et al. 2018).

Table 1. Total soluble solids (TSS), titratable acidity (TA), TSS/TA, total phenolic content (TPC), and total antioxidant capacity (TAC) of soursop after 7 d of storage at room temperature.

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The TPC and TAC of the control were 23% and 24% lower than the coated fruit, respectively (Table 1). TPC decreases at the climacteric peak of soursop (Paull 1982). Lower values for both in the control fruit reflect ripening-associated losses and delayed ripening in the coated sample relative to the control (Quirós-Sauceda et al. 2019). Lipid and polysaccharide coatings protect flavonoids by reducing respiration and ethylene synthesis (Kohli et al. 2024). Higher TPC and TAC in the coated sample suggests this effect is present in lipid-based coatings on soursop.

Both sample volatile profiles contained alcohols and esters with the alcohols 1-hexanol, hexen-3-ol, and nonanol uniquely present in the control sample (Table 2). These fermentation products reflected overripening and fermentation onset during storage in the control (Vázquez-Araújo 2023). Additionally, the relative abundance of ethanol in the control was greater than the coated fruit. This indicates that the coating may have delayed fruit degradation and the natural fermentation process of the fruit. Butanoic acid, 3-hydroxy, methyl ester (S), 3-octenoic acid, methyl ester (Z), and the hexenoic acid methyl esters found in the control are known microbial esterification products (Yu et al. 2022). The presence of linalool oxide may further indicate a loss of antioxidative activity in the control (Fu et al. 2024).

Table 2. Volatile compound profile for soursop after 7 d of storage.

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The coated fruit yielded higher TSS/TA, TPC, and TAC compared with the control. The presence of the alcoholic compounds 1-hexanol and 3-hexen-1-ol supports the physical observation that the control fruit progressed to a more advanced level of fermentation compared with the treated fruit. These results indicate that lipid-based coatings may extend the shelf life of tropical fruits such as soursop. Further experimentation based on current postharvest advances in temperature and humidity control to prolong storage may be merited. A combination of edible coatings and controlled environment storage may improve soursop’s viability for commercialization.