Usage of biological chitosan against the contamination of post-harvest treatment of strawberries by Aspergillus niger

Abstract

Developing bioactive food packaging, capable of extending the shelf life of fruits, has received increasing attention in recent years. The present study highlights the interest in post-harvest treatment for strawberries with chitosan as a preservation solution. Chitosan extraction was carried out from shrimp shells (Parapenaeus longirostris), composed of chitin, using citric acid during the demineralization step. Extracted chitosan was characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The presence of amino group (-NH2) in the obtained chitosan was confirmed by infrared (IR) spectral data. Deacetylation degree (DD), which has a value of 80.86%, was determined by FTIR spectra. X-ray diffraction pattern (XRD) showed two peaks of crystalline character, characteristic of extracted chitosan, approximately at 20° and 30° (2θ). Extracted chitosan morphology was studied by scanning electron microscopy (SEM) and showed a relatively smooth top surface and fibrous structures. Chitosan, acetic acid, and their interaction effects were evaluated on Aspergillus niger mycelial growth strain isolated from spoiled strawberries. Chitosan revealed a strong anti-fungal activity, dose-dependent (from 0 to 3%), on Aspergillus niger mycelial growth, while acetic acid showed moderate anti-fungal activity against the Aspergillus niger strain. Agri-food application was carried out using chitosan solubilized in acetic acid as a post-harvest treatment tool for the prolongation of shelf life of strawberries (by using an experimental design). Coating, with the developed preservative solution, significantly reduced microbial spoilage in strawberries. Treated strawberries retained their initial pigmentation for a longer period when compared to untreated strawberries. The treatment carried out maintained the cellular structures of treated strawberries during the storage period and thus extended the shelf life of strawberries which is considered very susceptible to reduce post-harvest losses.

Survey on technical management of strawberries in Morocco and evaluation of their post-harvest microbial load

“…In the same report, an attack by A. alternata was revealed on the samples analyzed with a percentage of contamination ranging from 19.8 to 23.4% depending on the varieties studied. A study done by El-araby et al (2022) reported that the fungal strain A. niger was isolated from spoiled strawberries.…”

Physicochemical Properties and Functional Characteristics of Ecologically Extracted Shrimp Chitosans with Different Organic Acids during Demineralization Step

“…Similar results have been obtained in previous studies. El-araby et al (2022) reported that the X-ray diffraction pattern of chitosan extracted from shrimp shells revealed two characteristic diffraction peaks at 2θ around 20° and 30°, which are typical fingerprints of crystalline chitosan character [ 26 ]. Another study reported that XRD studies of chitosan showed the maximum peak at 20.04° (113.92 counts/s), corresponding to chitosan crystalline nature [ 71 ].…”

“…Scanning electron microscopy (SEM) shows that chitosan produced from shrimp shells had a smooth and homogenous surface [ 25 ]. A study done by El-araby et al (2022) reported that the micrographs of shrimp shell chitosan showed a relatively smooth top surface and fibrous structures [ 26 ].…”

“…Afterward, discoloration was done with pure acetone at a ratio of 1:12 (g/mL) for 24 h under constant stirring (100 rpm). The resulting product was recovered, washed to neutrality, and then dried at 80 °C [ 26 ].…”

“…The purified chitin was deacetylated by 12.5 N sodium hydroxide (NaOH) at a ratio of 1:5 (g/mL). The deacetylation process was performed at 100 °C for 12 h. The chitosan obtained was filtered, washed with distilled water to neutrality, and completely dried at 80 °C [ 26 ].…”