Effects of sodium alginate coating and cold plasma treatment on biochemical changes, microbial load, and microstructure of 'Granny Smith' apples during storage

Abstract

Fresh apples are among the most important fruits, consistently in demand for their high nutritional quality; however, they have limited shelf-life under commercial handling conditions due to their active metabolic processes and associated quality loss. Hence, this study explored the impact of plasma-activated sodium alginate (SA) edible coating (CCP) on 'Granny Smith' apples, focusing on respiration rate (RRCO₂), physical and biochemical quality attributes, natural microbial load, and fruit surface morphology. The effects of CCP treatment were compared with apples only coated (CO), plasma treated (CP), and un-treated (Control) during five weeks at 15 °C storage. The results indicated that CCP treatment significantly reduced fruit weight loss and degradation of titratable acidity (TA) while preserving fruit firmness and color (a*) more effectively than the other treatments. Notably, all treatments (CO, CP, and CCP) significantly slowed down the RRCO₂ of apples (<i>p</i> = 0.000) and reduced total aerobic mesophilic bacteria count (<i>p</i> &lt; 0.001) compared to the control samples. The evaluation of the scanning electron microscopy (SEM) images of the 'Granny Smith' apple fruit surface demonstrated the presence of different patterns of the amorphous wax layer, and microcracks on control samples, whereas plasma treatment improved the homogeneity of sodium alginate coating on the fruit surface. This study demonstrated that plasma-activated coatings can enhance the quality of edible coatings, offering a promising alternative to conventional packaging material.