Metal-Based Nanoparticles in Food Packaging and Coating Technologies: A Review.

Food security has continued to be a topic of interest in our world due to the increasing demand for food. Many technologies have been adopted to enhance food supply and narrow the demand gap. Thus, the attempt to use nanotechnology to improve food security and increase supply has emerged due to the severe shortcomings of conventional technologies, which have made them insufficient to cater to the continuous demand for food products. Hence, nanoparticles have been identified to play a major role in areas involving food production, protection, and shelf-life extensions. Specifically, metal-based nanoparticles have been singled out to play an important role in manufacturing materials with outstanding properties, which can help increase the shelf-life of different food materials. The physicochemical and biological properties of metal-based nanoparticles, such as the large surface area and antimicrobial properties, have made them suitable and adequately useful, not just as a regular packaging material but as a functional material upon incorporation into biopolymer matrices. These, amongst many other reasons, have led to their wide synthesis and applications, even though their methods of preparation and risk evaluation remain a topic of concern. This review, therefore, briefly explores the available synthetic methods, physicochemical properties, roles, and biological properties of metal-based nanoparticles for food packaging. Furthermore, the associated limitations, alongside quality and safety considerations, of these materials were summarily explored. Although this area of research continues to garner attention, this review showed that metal-based nanoparticles possess great potential to be a leading material for food packaging if the problem of migration and toxicity can be effectively modulated.

Phenolic profiling and antioxidant evaluation of extracts from Southern African indigenous fruits byproducts.

The call to build climate-resilient food systems in Africa has revived interest in indigenous fruits, which, however, remain under-researched. In this study, the phenolic content and antioxidant profiles of seed and pulp of ethanolic extracts from eight Southern African indigenous fruits were evaluated using UPLC-ESI-Q-TOF/MS and four antioxidant assays. Total phenols and hydroxycinnamic acids were highest in Dovyalis caffra (Kei apple) seed (5084.5 and 3403.83 mg/kg). Flavonoids were most abundant in Colpoon compressum (Colpoon) seed (1127.23 mg/kg), while hydrolysable tannins were highest in Syzygium guineense (Water pear) seed (666.13 mg/kg). Proanthocyanidins were abundant in Harpephyllum caffrum (Wild plum) pulp while anthocyanins were highest in Olea africana (Wild olive) pulp. Hierarchical clustering heatmap analysis showed similar concentration and diversity in the composition of reported compounds. Syzygium guineense seed had the lowest DPPH values. ORAC values were highest in O. africana pulp while H. caffrum pulp had the highest FRAP values and lipoxygenase inhibition capacity. In conclusion, the study revealed a diverse profile of phenolics in indigenous fruits extracts, to which their bioactivity is attributed. Specifically, H. caffrum pulp and S. guineense seed have potential as natural sources of phenolic antioxidants for food application.

Biopreservative efficacy of grape (Vitis vinifera) and clementine mandarin orange (Citrus reticulata) by-product extracts in raw ground beef patties.

Beef patties were treated with 450 µg/g of extracts from grape (Vitis vinifera) seeds (GSE), pomace (GPE) or orange (Citrus reticulata) pomace (OPE) and compared to negative (no extract; CTR) and positive (sodium metabisulphite; SMB) controls for their effect on colour, lipid and protein oxidation and bacterial growth under simulated retail display conditions (4 °C) for 9 d, and sensory quality. Antioxidant activity and redness of beef patties increased in the order of CTR < OPE = GPE < GSE < SMB. The order of thiobarbituric acid reactive substances and carbonyl values were CTR > GPE = OPE > GSE > SBM, while that of bacterial counts were CTR > GSE = GPE > OPE > SMB. Retail display period had significant effect on all the shelf-life parameters. Overall, intensity of aroma, beef-like aroma and flavour in beef patties were highest in OPE. Results suggested that GSE and OPE could be commercially valorised as natural antioxidants and antibacterials in beef patties, respectively.

Applications of Cytokinins in Horticultural Fruit Crops: Trends and Future Prospects.

Cytokinins (CKs) are a chemically diverse class of plant growth regulators, exhibiting wide-ranging actions on plant growth and development, hence their exploitation in agriculture for crop improvement and management. Their coordinated regulatory effects and cross-talk interactions with other phytohormones and signaling networks are highly sophisticated, eliciting and controlling varied biological processes at the cellular to organismal levels. In this review, we briefly introduce the mode of action and general molecular biological effects of naturally occurring CKs before highlighting the great variability in the response of fruit crops to CK-based innovations. We present a comprehensive compilation of research linked to the application of CKs in non-model crop species in different phases of fruit production and management. By doing so, it is clear that the effects of CKs on fruit set, development, maturation, and ripening are not necessarily generic, even for cultivars within the same species, illustrating the magnitude of yet unknown intricate biochemical and genetic mechanisms regulating these processes in different fruit crops. Current approaches using genomic-to-metabolomic analysis are providing new insights into the in planta mechanisms of CKs, pinpointing the underlying CK-derived actions that may serve as potential targets for improving crop-specific traits and the development of new solutions for the preharvest and postharvest management of fruit crops. Where information is available, CK molecular biology is discussed in the context of its present and future implications in the applications of CKs to fruits of horticultural significance.

The Implication of Chemotypic Variation on the Anti-Oxidant and Anti-Cancer Activities of Sutherlandia frutescens (L.) R.Br. (Fabaceae) from Different Geographic Locations.

Extracts of Sutherlandia frutescens (cancer bush) exhibit considerable qualitative and quantitative chemical variability depending on their natural wild origins. The purpose of this study was thus to determine bioactivity of extracts from different regions using in vitro antioxidant and anti-cancer assays. Extracts of the species are complex and are predominantly composed of a species-specific set of triterpene saponins (cycloartanol glycosides), the sutherlandiosides, and flavonoids (quercetin and kaempferol glycosides), the sutherlandins. For the Folin-Ciocalteu phenolics test values of 93.311 to 125.330 mg GAE/g DE were obtained. The flavonoids ranged from 54.831 to 66.073 mg CE/g DE using the aluminum chloride assay. Extracts from different sites were also assayed using the 2,2-diphenyl-1-picrylhydrazyl (DPPH•) radical scavenging method and ferric reducing anti-oxidant power (FRAP) methods. This was followed by an in vitro Cell Titer-Glo viability assay of various ecotypes using the DLD-1 colon cancer cell line. All test extracts displayed anti-oxidant activity through the DPPH• radical scavenging mechanism, with IC50 values ranging from 3.171 to 7.707 µg·mL-1. However, the degree of anti-oxidant effects differed on a chemotypic basis with coastal plants from Gansbaai and Pearly Beach (Western Cape) exhibiting superior activity whereas the Victoria West inland group from the Northern Cape, consistently showed the weakest anti-oxidant activity for both the DPPH• and FRAP methods. All extracts showed cytotoxicity on DLD-1 colon cancer cells at the test concentration of 200 µg·mL-1 but Sutherlandia plants from Colesburg (Northern Cape) exhibited the highest anti-cancer activity. These findings confirm that S. frutescens specimens display variability in their bioactive capacities based on their natural location, illustrating the importance of choosing relevant ecotypes for medicinal purposes.

Effect of drying on the bioactive compounds, antioxidant, antibacterial and antityrosinase activities of pomegranate peel.

BACKGROUND: The use of pomegranate peel is highly associated with its rich phenolic concentration. Series of drying methods are recommended since bioactive compounds are highly sensitive to thermal degradation. The study was conducted to evaluate the effects of drying on the bioactive compounds, antioxidant as well as antibacterial and antityrosinase activities of pomegranate peel. METHODS: Dried pomegranate peels with the initial moisture content of 70.30 % wet basis were prepared by freeze and oven drying at 40, 50 and 60 °C. Difference in CIE-LAB, chroma (C*) and hue angle (h°) were determined using colorimeter. Individual polyphenol retention was determined using LC-MS and LC-MS(E) while total phenolics concentration (TPC), total flavonoid concentration (TFC), total tannins concentration (TTC) and vitamin C concentration were measured using colorimetric methods. The antioxidant activity was measured by radical scavenging activity (RSA) and ferric reducing antioxidant power (FRAP). Furthermore, the antibacterial activity of methanolic peel extracts were tested on Gram negative (Escherichia coli and Klebsiella pneumonia) and Gram positive bacteria (Staphylococcus aureus and Bacillus subtilis) using the in vitro microdilution assays. Tyrosinase enzyme inhibition was investigated against monophenolase (tyrosine) and diphenolase (DOPA), with arbutin as positive controls. RESULTS: Oven drying at 60 °C resulted in high punicalin concentration (888.04 ± 141.03 mg CE/kg dried matter) along with poor red coloration (high hue angle). Freeze dried peel contained higher catechin concentration (674.51 mg/kg drying matter) + catechin and -epicatechin (70.56 mg/kg drying matter) compared to oven dried peel. Furthermore, freeze dried peel had the highest total phenolic, tannin and flavonoid concentrations compared to oven dried peel over the temperature range studied. High concentration of vitamin C (31.19 µg AAE/g dried matter) was observed in the oven dried (40 °C) pomegranate peel. Drying at 50 °C showed the highest inhibitory activity with the MIC values of 0.10 mg/ml against Gram positive (Staphylococcus aureus and Bacillus subtili. Likewise, the extracts dried at 50 °C showed potent inhibitory activity concentration (22.95 mg/ml) against monophenolase. Principal component analysis showed that the peel colour characteristics and bioactive compounds isolated the investigated drying method. CONCLUSIONS: The freeze and oven dried peel extracts exhibited a significant antibacterial and antioxidant activities. The freeze drying method had higher total phenolic, tannin and flavonoid concentration therefore can be explored as a feasible method for processing pomegranate peel to ensure retention of the maximum amount of their naturally occurring bioactive compounds. TRIAL REGISTRATION: Not relevant for this study.

Effects of different maturity stages and growing locations on changes in chemical, biochemical and aroma volatile composition of 'Wonderful' pomegranate juice.

BACKGROUND: This study investigated the changes in chemical attributes of pomegranate fruit such as total soluble solids (TSS), titratable acidity (TA), TSS/TA ratio, pH, individual compounds (organic acids and sugars) and volatile composition as affected by fruit maturity status and growing location (Kakamas, Koedoeshoek and Worcester in South Africa). Headspace solid phase microextraction coupled with gas chromatography/mass spectrometry was used for volatile analysis. RESULTS: A significant increase in TSS from 14.7 ± 0.6 to 17.5 ± 0.6 °Brix was observed with advancement in fruit maturity, while TA decreased from 2.1 ± 0.7 to 1.1 ± 0.3 g citric acid per 100 mL across all agro-climatic locations investigated. Fruit TSS/TA ratio and pH increased from 7.8 ± 2.6 to 16.6 ± 2.8 and from 3.3 ± 0.1 to 3.6 ± 0.2 respectively during fruit maturation across all agro-climatic locations. Fructose and glucose concentrations increased continually with fruit maturity from 69.4 ± 4.9 to 91.1 ± 4.9 g kg(-1) and from 57.1 ± 4.7 to 84.3 ± 5.2 g kg(-1) respectively. A total of 13 volatile compounds were detected and identified, belonging to five chemical classes. The most abundant volatile in unripe and mid-ripe fruit was 1-hexanol, while 3-hexen-1-ol was highest at commercial maturity. CONCLUSION: Knowledge on the impact of fruit maturity and agro-climatic locations (with different altitudes) on biochemical and aroma volatile attributes of pomegranate fruit provides a useful guide for selecting farm location towards improving fruit quality and the maturity stage best for juice processing.

Antibacterial, antioxidant and tyrosinase-inhibition activities of pomegranate fruit peel methanolic extract.

BACKGROUND: This study evaluated, using in vitro assays, the antibacterial, antioxidant, and tyrosinase-inhibition activities of methanolic extracts from peels of seven commercially grown pomegranate cultivars. METHODS: Antibacterial activity was tested on Gram-positive (Bacillus subtilis and Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli and Klebsiella pneumonia) using a microdilution method. Several potential antioxidant activities, including radical-scavenging ability (RSA), ferrous ion chelating (FIC) and ferric ion reducing antioxidant power (FRAP), were evaluated. Tyrosinase enzyme inhibition was investigated against monophenolase (tyrosine) and diphenolase (DOPA), with arbutin and kojic acid as positive controls. Furthermore, phenolic contents including total flavonoid content (TFC), gallotannin content (GTC) and total anthocyanin content (TAC) were determined using colourimetric methods. HPLC-ESI/MSn analysis of phenolic composition of methanolic extracts was also performed. RESULTS: Methanolic peel extracts showed strong broad-spectrum activity against Gram-positive and Gram-negative bacteria, with the minimum inhibitory concentrations (MIC) ranging from 0.2 to 0.78 mg/ml. At the highest concentration tested (1000 µg/ml), radical scavenging activities were significantly higher in Arakta (83.54%), Ganesh (83.56%), and Ruby (83.34%) cultivars (P< 0.05). Dose dependent FIC and FRAP activities were exhibited by all the peel extracts. All extracts also exhibited high inhibition (>50%) against monophenolase and diphenolase activities at the highest screening concentration. The most active peel extract was the Bhagwa cultivar against monophenolase and the Arakta cultivar against diphenolase with IC50 values of 3.66 µg/ml and 15.88 µg/ml, respectively. High amounts of phenolic compounds were found in peel extracts with the highest and lowest total phenolic contents of 295.5 (Ganesh) and 179.3 mg/g dry extract (Molla de Elche), respectively. Catechin, epicatechin, ellagic acid and gallic acid were found in all cultivars, of which ellagic acid was the most abundant comprising of more than 50% of total phenolic compounds detected in each cultivar. CONCLUSIONS: The present study showed that the tested pomegranate peels exhibited strong antibacterial, antioxidant and tyrosinase-inhibition activities. These results suggest that pomegranate fruit peel could be exploited as a potential source of natural antimicrobial and antioxidant agents as well as tyrosinase inhibitors.