Development of Process Technology for Valorization of Pomegranate Peel and its Application in Powdered Infant Formula

Infants have a low developed immune system, which raises the possibility of microbial infections when exposed to contaminated foods. Infant foods, especially powdered infant formula (PIF), have been epidemiologically linked with various food-borne infections. Staphylococcus aureus is one of the major pathogens that could be related to these infant food outbreaks. Though traditional thermal processing and the use of synthetic antibiotics effectively kill food-borne pathogens, they have been found to degrade quality attributes that are objectionable to consumers. To resolve this issue, notable efforts have been taken, among which the use of natural antimicrobials is the foremost approach. Pomegranate peels are known to exhibit various groups of phytochemical compounds consisting of polyphenols, anthocyanins, flavonoids, phenolic acids, and hydrolysable tannins at significant levels compared to fruit arils. The hydrolysable tannins present within pomegranate peel have been known for their noteworthy antimicrobial properties. However, owing to the lack of proper value addition methods, the antimicrobial property of pomegranate peels is not still utilized to their full potential. This urges the need to develop a process technology that could utilize pomegranate peels as a robust natural antimicrobial compound. In the present work, a process protocol is being developed that aids to determine the antimicrobial activity of encapsulated pomegranate peel extract against strains of S. aureus isolated from PIF. Unit operations namely drying, grinding, extraction and encapsulation are vital for the appropriate use and value-addition of the pomegranate peels as a natural antimicrobial. For the maximum recovery of phytochemical compounds, the fresh pomegranate peels were dried using the microwave vacuum drying method. The drying experimental runs were performed on varied ranges of microwave power (175, 330, 485 W) and vacuum pressure (10, 15, 20 kPa) using a face‐centered composite design. Optimized condition for microwave- vacuum drying of pomegranate peel (within the chosen range) was observed as 276 W microwave power and 10 kPa vacuum. At the optimized condition, the phytochemical compounds targeted were considerably preserved. Amino acid analysis of dried peels at optimized conditions exhibited the retention of 11 amino acids at significant levels with glycine possessing the highest concentration 5.93 mg/g. The dried pomegranate peel was ground using conventional and cryogenic grinding techniques. From the numerous powder properties studied, say bulk density, true density, porosity, product temperature, moisture content, water activity, phytochemical compounds, and surface morphology analysis, it was concluded that the properties of the cryogenically ground peel powders were superior to that of the conventionally produced peel powders. The extract from cryogenically ground pomegranate peel powder, containing maximum phytochemical compounds (with the highest recovery of hydrolysable tannins) was extracted using pulsed system ultrasound. The process variables in total hydrolysable tannin extraction were modeled and optimized by an artificial neural network and genetic algorithm respectively. The optimal extraction conditions attained for process variables were; solvent concentration of 56%, solvent-feed ratio of 26.5 mL/g, extraction time of 15 min, and ultrasound amplitude of 50% respectively. Pulsed system ultra-sonication significantly augmented total hydrolysable tannins of pomegranate peel extract to 98.12 mg TAE/g compared to 50.14 mg TAE/g with conventional extraction. The Fourier transform infrared spectroscopy (FTIR) and high performance liquid chromatography (HPLC) analyses established that pomegranate peel extract produced at above optimal conditions contained a significant amount of hydrolysable tannin compounds (gallic acid and tannic acid derivative) than conventional extraction methods. The pomegranate peel extract was encapsulated using external gelation technique. The process variables in encapsulation were modeled and optimized by Box-Behnken design. The encapsulation efficiency and properties of encapsulate were found to be optimum at 4% sodium alginate concentration, 2.5% CaCl2 concentration, and 30% PPE concentration. The encapsulation efficiency at the optimized condition was 83.65%. A comparative study was performed to evaluate the properties of encapsulates produced by external gelation (at its optimum conditions) and spray drying. The encapsulates were analyzed for various physical properties, phytochemical parameters, release profile, storage stability, and thermal stability. The performed analyses revealed the superiority of the encapsulates produced by external gelation over spray drying. Further the thermal stability and antibacterial activity of developed pomegranate peel extract encapsulates was carried out. The outcomes revealed that the zone of inhibition (ZOI) and minimum inhibitory concentration (MIC) of encapsulated pomegranate peel extract against S. aureus (ATCC 25923) identified in PIF were 32 ± 0.01 mm, and 300 μg/mL respectively. The outcomes are promising and recommend the possibility of utilizing encapsulated pomegranate peel extract as natural antimicrobials or as a systemic natural antibiotic replacing the synthetic antibiotics for inactivation of S. aureus strains isolated from powdered infant formula at an industrial level