The increase in human population and the anticipated further increase incorporated with increase in households that earn higher income, thus, can afford to buy meat is forcing the meat industry to grow and produce meat rapidly [1]. The demand is weighing more on chicken meat as it is by far leading in consumption increase due to its affordability. In attempts to produce meat rapidly and meet profit margins, stocking density is increased from the welfare recommended 10 birds per m² to more than 15 birds per m² with projected 1.8 kg slaughter weights [2]. The increased stocking density assists with producing more meat per square metre, thus, greater chances of meeting profit margins. The increased stocking density, however, further deteriorates the relatively short broiler meat shelf life. Increased free radicals from greater reactive oxygen species (ROS) that oxidise the abundant polyunsaturated fatty acids (PUFA) [3,4]. To scavenge the free radical’s synthetic antioxidants are applied.

Synthetic antioxidants such as butylated hydroxy anisole, butylated hydroxy toluene, and synthetic tocopherol are being added to stabilize free radicals and delay nutrient oxidation. Adding synthetic antioxidants to reduce oxidative damage, however, may potentially cause adverse health effects and consumers prefer natural antioxidants, therefore, it remains a challenge to the meat industry [5,6]. In response to this challenge, research has shifted towards the investigation of natural antioxidants which are important in maintaining health [7]. Pre-harvested plant-derived antioxidant have been used to minimize oxidation in meat products [8], however, one source may not be sufficient in efficiently reducing oxidation. Polyphenols with assistance from amino acids may act as enhanced antioxidants, however, individually may not be efficient. Polyphenols may also enhance essential oils’ ability to reduce microorganisms. Varying flavonoids may disrupt microbiota membrane to inhibit the growth of microorganisms and chelate metal leading oxidation inhibition [9–11]. The use of multiple sources instead of one may, thus, yield improved meat shelf-life due to synergetic relationships amongst antioxidants that may render them superior to single ingredient antioxidants. Blending specific chemical compounds may lead to further synergetic action which further improves meat shelf-life [12,13].

Natural antioxidants sources include legumes, tree leaves, cereals, fruits, seeds, spices, vegetables, teas, and herbs [14,15]. Cereals, fruits, and vegetables form the greater part of a human diet, thus would create food-feed competition. Legumes, teas, and trees are rich in phenols, tannins, flavonoids, vitamins that have antioxidant properties and a minimized food-feed competition. High polyphenolic compound inclusion reduces growth performance in broilers before enough polyphenols are incorporated into the meat. The amount incorporated, however, is sufficient to reduce the effect of ROS at growth [16,17]. Marinating broiler meat with the leaf meal and leaf meal extracts may, therefore, provide a more concentrated form of polyphenols, thus, leading to more polyphenols in the meat [18,19].

Adding natural antioxidants may reduce the rapid oxidation of protein and extend nutritional shelf-life. The rapid alteration in visual appearance during storage would be reduced and an improved quality product would motivate consumers to trust and buy the meat [20]. The reduced shelf-life that is a cause for concern for meat retailers, wholesalers, and consumers while transitioning in the supply chain would be combated. Meat being partially spoiling whilst consumers are travelling home may be improved at disadvantaged communities along improved nutrients quantity of nutrients. The development of off flavours and deterioration of meat colour may also be delayed. This review, thus, aims to present and evaluate the potential of processing broiler meat with plant derived leaf meal antioxidants on improving shelf-life and human health.

The global meat industry is constantly evolving because of consumer preference change, lifestyle concerns, monetary, geographical, political, cultural, religious factors and food loss and waste [8]. Most variable loss and waste occur during handling, storage, processing, distribution, market, and consumption level depending on region [21]. Remarkably, farmers are reducing losses; however, it is evident that most developed countries lose more meat at consumption and developing countries loose meat as early as processing [22]. The loss in profits in developing countries is distributed amongst processors, wholesalers, and greatly consumers. This implies that exporting fresh produce for developing countries is not feasible, however, importing from developed countries is possible. This then leads to more loss in meat in developing countries as they cannot export chicken breasts that most developed countries prefer as fresh meat. Developing countries have made vacuum packed meat more expensive, thus, less people afford the meat leading to more retail loss. Methods such as meat salting, canning, fermentation, and smoking were also put to use to extend shelf life, however, may had not been effective enough [23].

The industry has added cold logistical chains, thermal treatment which includes super chilling, ultrarapid freezing, immersion vacuum cooling, pressure-shift freezing, dielectric heating and ohmic heating to extend shelf-life. In efforts to increase consumer safety, meat quality and nutritional shelf-life; traditional cutting and paper or waxed paper wrapping was replaced by store cutting and display on packages in fridges for self-service [23]. Packaging has also modified package atmosphere by vacuum ceiling, active packaging, and smart packaging [23]. These methods are, however, still challenged by the initial microbial load which hinder the preservation of meat nutrients at storage [24]. The other concern is skilled enough workers to handle the meat correctly. More than 3.5 billion kg per annum of poultry and meat is wasted at the consumer, retailer and foodservice levels and mainly attributed to microbial spoilage [25]. Increasing shelf-life could potentially save 5% of this meat and that could potentially feed more than 300,000 people. The added oxidative stress from heat stress and a greater stocking density also adds to the yet to be resolved shelf-life issue.

Various literature has established the potential capacity of plant derived natural antioxidants to delay oxidation process and extend the shelf-life of meat products. Poultry producers have been encouraged to use natural antioxidant, such as, natural dietary alternatives and plant extracts to reduce the negative effect of lipid and protein oxidation. Plants extracts rich in polyphenol are known for several health benefits, examples being, Punica gratun L species which is rich in polyphenolic compounds and flavonoids reduces lipid oxidation in human bladder cells [26]. This necessitates research that focuses on using natural antioxidants from plant sources to replace synthetic antioxidants in the poultry industry. The effects of natural antioxidants, however, depend on various factors which include plants state when being utilized.

Plants amino acids and minerals are reduced as the plant ages, however, pre-harvest they are greater than after processing. Polyphenols increase as the plant ages pre-harvest, thus, the chemical component the plant is needed for is important. This also demonstrates that one plant may not be ideal for the best antioxidants’ composition and capability. The use of plants at a younger age may assist improve shelf-life by providing amino acids and minerals which may scavenge free radicals, such as, carbonyls leading to a greater meat colour, tenderness, juiciness, and off odour shelf-life. This, however, would not scavenge sufficient hydroxyls, peroxyls and alkyl radicals which ultimately lead to the carbonyls, hydroperoxides, hydrocarbons and alcohols produced by protein oxidation. Ultimately, the shelf-life of the meats’ nutritional value, flavour, tenderness, and colour is not efficiently extended. The consumers recurring purchase may also be reduced by the reduction in flavour, tenderness, and colour.

Polyphenols assist with hydrogen abstraction; their reduction may lead to a reduced hydrogen abstraction efficiency, thus, greater autoxidation and deteriorated fatty acid profile. Amino acids may have a weak antioxidant capability; however, amino acids improve polyphenols’ ability to scavenge on free radicals leading to an efficient oxidation reduction in meat fats and protein. Polyphenols and essential oils have a synergistic relationship that reduces microbial load which may ultimately extend shelf-life. The use of blended sources has been documented to be superior to individual sources, thus, fresh leaves may be difficult to incorporate [27]. Extracting fresh leaves has been documented to have lower antioxidant capacity compared to air dried plant material. The time of the year the plant is being harvested at is, however, also essential as harvesting during dry season may lead to plants with greater polyphenols than when harvested in a wet season. The expense in feeding natural antioxidants extracts may be high leading to a hike in production costs. Various antioxidant application methods for improved meat quality, therefore, need to be explored. Individual leaf meals influence few parameters, blending them may produce an improved shelf-life extension.

As plants dry, their antioxidant capacity is significantly reduced. There was a 6.4% loss in antioxidant capacity for celery vegetable plants dried by air and 33.7% for coriander dried by oven [28]. Some plants species show a positive correlation between antioxidant activity and vitamin C, vitamin E, and beta-carotene content [28]. The phenol, carotenoids, chlorophyll, and antioxidant capacity of fresh plants are higher than that of dried plants. A plant’s maturity stage affects its polyphenol content and overall quality. For instance, strawberry accumulates flavanols at high levels during early stages, whereas anthocynanins synthesis starts later and is most abundant when berries are ripe [29]. Karlund et al [29] found that total phenolics, total flavonoids, and total antioxidant activity were higher at the pink stage than at the ripe stage.

Lipid oxidation, protein oxidation, and meat spoilage bacteria are the main contributors to the reduction in the shelf-life of meat; thus, these leaf meal characteristics may be beneficial. Oxidation reduces the nutritional value of meat by deteriorating essential fatty acids, proteins leading to an unacceptable flavour, and toxins generation. Oxidation of meat in human leads to the nutrients losing its function causing disorders, such as, cancer, diabetes, obesity, dysfunction of red blood cells, and heart diseases. Bacteria, such as, Pseudomonas spp. and Lactobacillus spp. lead to off odour, discoloration, gas production, slime production and pH reduction [30]. Application of antioxidants and antimicrobials maintains the quality and safety of meat while also extending shelf-life and spoilage time [31,32]. Plant based antioxidants, however, need to be harvested and processed carefully to ensure high antioxidant capacity.

Blending of antioxidants sources may be superior as it would allow the use of various plant sources which assists with keeping the environmental resources at balance. Further, increases sources may increase chances of high radical affinity antioxidants threshold is met to optimize antioxidation in meat. It is noteworthy that synergic relationships may occur between chemical components within a leaf meal and between leaf meals as most these relationships are chemically related. It is also, however, evident that minimal plants have sufficient within plant synergic relationships to efficiently improve meat quality and shelf-life.

The effects various antioxidant sources have on meat which is not limited to shelf-life, however, limited to parameters that determine shelf-life. Oreganos’ documented effect is its antibacterial activity which may increase shelf-life [33–35]. Rosemary stabilizes redness, reduces oxidation and enhanced meat flavour. Clove improves water holding capacity, reduces thiol groups and thiobarbituric acid reactive substances (TBARS) and increases redness. This, however, does not guarantee that the redness is stabilised as it is increased. Blending clove, rosemary and oregano may lead to greater shelf-life extension as they all have varying characteristics which all contribute to an extended shelf-life. These spices, however, may be limited to certain areas and costly at other areas.

Umsasane (Vachellia tortilis) (high flavonoid), Umunga (Vachellia karroo) (low flavonoids), Paperback thorn (Vachellia sieberiana), babul (Vachellia nilotica) (medium flavonoids), Moringa (Moringa oliefera), uMhlonyane (Artemisia afra) (medium flavonoids), Buffalo thorn, Umphafa (Ziziphus mucronata) (low flavonoids), Rooibos (Aspalathus linearis) (high flavonoids) are potential plants that may be blended. They have not been studied extensively, however; the minimal studies published have demonstrated their potential if blended as they have antimicrobial and antioxidant capabilities. Blending these various antioxidant sources may yield superior shelf-life compared to individual sources.

The increase in the various antioxidant sources may lead to synergetic effects and strategic selection of sources may also be advantageous [36]. Considering current use of the plant material and their availability; these plants have a potential to be produced at a large scale and are already readily available at a wide scale. They also have minimal or natural aroma, thus, may induce neglectable undesirable odour in the meat. The optimal concentrations at which the leaf meals should be included is difficult to estimate as their chemical composition is not well studied, and synergic effects are complicated and hard to predict. The method used to apply antioxidants may not be effective or lead to consumer negative response to products which is the challenge the industry is currently encountering. Blending antioxidants would ensure a sustainable environment and complement one another once desirable concentrations have been established.

The addition of polyphenols in efforts to improve broiler meat quality and increase meat shelf-life should be explored more to reduce loss/waste of meat. Using polyphenols as marinade may increase broiler meat shelf-life by at least 3 days which may be longer with varying antioxidant sources. Feeding and marinating the meat may be advisable as feeding is a first line of defence during rearing and when enzymes are defeated nutritional components and antioxidants may be of assistance. Meat shelf-life parameters, such as, redness are hard to extend as the metmyoglobin formation delay has not been well studied. The inclusion of medicinal plants may, however, have an added advantages as they may prevent or reduce humans’ susceptibility to a wide range of sickness. Marinating broiler meat with medicinal plants which are not widely used may assist maintain biodiversity and combat sickness in humans. It is, therefore, advisable to use these hardly used bush encroaching plants for human benefits. More studies, however, need to be conducted to determine which antioxidant combination works better on which parameters and/or microbes. An extensive chemical composition of polyphenols especially of V. karroo, V. nolitica, Artemisia afra, Ziziphus mucronate, V. tortilis and rooibos need to be explored to make it easier to extrapolate how they may affect meat shelf-life once polyphenol combination is established. Concentrations needed of these leaf meals and of individual polyphenols to be combined are also essential and need more attention.