Development of zinc oxide nanoparticles as safe coating for the shelf life extension of grapes (Vitisvinifera L., Red Globe) fruits

Abstract

The effects of zinc oxide nanoparticles coating (NZO) developed from chitosan (CH) with incorporation of bergamot essential oil (BO) were investigated to extend the shelf life of grapes (Vitisvinifera L., Red Globe). Treated and untreated grapes were determined for some postharvest and phytochemical properties such as decay incidence, firmness, polyphenol oxidase enzyme activity (PPO), proximate analysis, and sensory evaluations. Besides, that microbial growth against S. typhimurium bacteria was also evaluated during 16 days of storage period of grapes at 25 °C. Descriptions of coating treatments were the following; control “COL” (distilled water/glycerol (1%)/acetic acid (0.5%)); chitosan “CH” with priority 85% (1%), distilled water/glycerol (1%)/acetic acid (0.5%); chitosan/nano zinc oxide (1%), partial size of (15 nm) “CH-NZO;” chitosan/nano zinc oxide/bergamot oil (1%) “CH-NZO-BO.” The control treated berries started to rot after 7 days; the noted highest corruption on 16th day s of storage (32.51). While CH berries coated became rotten after 9 days, those coated with CH–NZO and CH–NZO–BO achieved the lowest decay incidence percentage with no remarkable differences after 16 days (10.11% and 9.13%), respectively. The loss of firmness value was more seriously considered for the COL berries 3.84 N after the 16th day. On the other hand, the highest firmness value was for CH–NZO–BO which recorded 8.27 N. In the same trend, CH and CH–NZO achieved similar values after 16 days (6.31 N and 6.98 N), respectively. The lowest PPO activity was observed for COL berries at 0.31 Unit/Minute after 16 days of storage. Though, the highest activity was recorded by CH–NZO–BO treatment at 0.99 Unit/Minute. The content of proteins was between 2.32 and 3.04%, fats between 0.30 and 0.43%, and total carbohydrates between 78.47 and 78.65% on the 16th day of storage. The highest reduction in the numbers of microbial growth 2.78 Log CFU/Berry occurred by coating with CH–NZO–BO at the end of the storage period, while no inhibition was detected with COL and CH treatments which recorded 4.99 and 4.69 Log CFU/Berry, respectively. The visual aspect in COL samples showed a serious reduction of 1.10 with high rates of dehydration and browning, while CH-NZO–BO samples showed the highest rate of 4.33. CH–NZO–BO samples also showed a relatively high rate of firmness of 4.11, crunchiness of 3.92, and sourness of 3.53. CH–NZO recorded the highest rates for juiciness 4.15 and sweetness 3.51. Though, the CH–NZO–BO coating can be recommended for food industry.