Promising natural extracts for use in active food packaging

Abstract

Food waste is a significant problem worldwide, with approximately one third of all food produced spoiling before consumption. One way that this food spoilage problem can be addressed is through active packaging – packaging that does more than act as a passive barrier. By introducing antioxidant and antimicrobial compounds into the packaging, bacteria and free radical scavengers can be prevented from affecting food. However, consumers are becoming more environmentally aware and the acceptability of synthetic compounds is declining. Natural extracts that still provide the antioxidant and antimicrobial benefits are one solution. Added value can be attained by using waste products to produce these extracts. Winery waste, also known as grape marc, is the by-product of the wine industry. It consists of grape skins, seeds, and stems, and has a high phenolic content, which is known to provide antioxidant and antimicrobial activity. The aim of this thesis was to explore the properties of natural extracts and their potential application in active food packaging. To this end, grape marc was used to produce grape marc extracts (GME) rich in polyphenols. First, different extraction methods were compared, and a conventional solvent extraction was used due to its simplicity and low-cost. Biodegradable and bio-sourced films were then used as proof of concept for GME activity in films. Ethyl cellulose, fish gelatin, and soy protein isolate (SPI) films were produced at low temperature and showed good free radical scavenging with the addition of 2% GME. Ethyl cellulose films also showed activity against Staphylococcus aureus. Most of the packaging used worldwide is linear low-density polyethylene (LLDPE) or high-density polyethylene (HDPE). These polymers are processed at temperatures above 150 ˚C, and so the heat tolerance of GME for use with these polymers was investigated. The heating of GME to temperatures up to 200 ˚C did not significantly degrade the phenolic compounds, nor did it affect the free radical scavenging ability or antimicrobial activity against S. aureus or Escherichia coli. A small amount of degradation was found in GME heated to 250 ˚C. Finally, the work with GME made way for an investigation into the potential development of antifungal active packaging. A wide range of natural extracts and essential oils (EO) were investigated for their activity against the key microorganisms in bread spoilage: fungi Aspergillus brasiliensis and Penicillium citrinum, and yeast Pichia burtonii. Six extracts or oils were shortlisted for further testing, chosen for their activity, New Zealand connection, and heat tolerance. Finally, three extracts were incorporated into LLDPE films. One essential oil was then discounted due to sensory issues that would be incompatible with the target application. However, the antifungal activity did not transfer to the films, although the films did show improved free radical scavenging abilities.