Story by Dr Evangelia Komitopoulou, global technical manager – food, SGS.
An increasing number of foods with ‘functional’ properties and health benefits have emerged in recent years mainly driven by public demand for health-related products. At the same time, the scientific understanding of the beneficial health effects of newly marketed botanical products, bio-actives and other ‘natural’ ingredients has significantly improved.
A lot of attention has been drawn to whole products, such as cranberry and whole grain oats, with nutritional and health benefits; products derived from plants, such as soya and tomato extracts used as sources of isoflavone-based estrogenic activity and a source of the antioxidant lycopene, respectively; as well as on the use of products used in traditional medicine (eg ginseng extract).
Although there is generally limited evidence of any prior history of human consumption, the latter has increasingly been considered for food applications.
Use of plant-derived ‘natural’ products and ingredients in food applications would require that certain critical factors related to their source and extraction/processing are taken into consideration. Plant species identification is considered to be a critical factor that can affect the safety of the ingredient per se as well as that of the food product in which the ingredient will be used.
Knowledge of the part of the plant that the material was extracted from is very important in order to determine the likelihood of toxic compounds being present in the preparation and to account for any variability in composition. The latter may also be a result of seasonality or differences in the extraction procedures followed, which usually account for notable differences in the quantity and proportion of key constituents that can affect the safety or health or other benefits associated with the material (eg Schilter et al, 2003).
Plant-derived ingredients have been extensively studied for their antimicrobial properties targeting a range of food-borne pathogens and spoilage microorganisms with the aim to provide ‘natural’ alternatives to chemical synthetics used in food and drink preservation. Chemical preservatives are generally considered cheap and effective.
Preservatives such as benzoates, nitrites, sulphites and sorbates seem to be the best and most effective. However, a number of different health scares have surfaced around the use of these preservatives. Examples include, in 2006, the presence of sodium benzoate being linked to benzene formation in the presence of ascorbic or citric acid, while the consumption of mixes of certain artificial food colour with sodium benzoate was linked to an adverse effect on children’s behaviour.
Chemically synthesised preservatives have been around for many years, and they can be applied in a one-size-fits-all manner. Currently, there are only a few ‘natural’ antimicrobials that can be used as direct replacements of existing chemical synthetics, since they are generally regarded as not being as effective, prove to be too costly, have adverse sensory characteristics or significantly affect the quality of the food product.
Not all natural antimicrobial compounds are suitable for use in all types of foods and under all conditions, However, despite their limitations and challenges to their use, further research into alternative preservative solutions has so far indicated that some compounds have great potential to function as effective barriers to the growth of pathogenic and spoilage micro-organisms in foods.
Green tea (GTE) and grape seed extracts (GSE) are two popular examples of plant extracts that have received significant experimental, application and consumer attention with respect to their potential uses as ‘natural’ food ingredients.
They are considered popular natural sources of antioxidants and antimicrobial compounds, as well as having other health benefits, eg anti-inflammatory and anti-carcinogenic properties, with a potential to improve food safety and quality.
Given that in most cases antimicrobial activity is a synergistic effect, ie a result of multiple hurdles applied to any one product, their antimicrobial/preservative properties have been shown to have a significant impact on the microbiological quality and safety in a number of different food applications such as raw and cooked meat, fish, poultry products, fresh produce, etc. when used in combination with bacteriocins, organic acids (lactates, acetates etc) vacuum packaging, pH, storage temperatures etc.
Green tea catechins have demonstrated significant antioxidant properties in a variety of food applications and were previously shown to inhibit and/or delay lipid oxidation in red meat and poultry patties without having any adverse effects on their sensory characteristics, thus contributing to enhanced product quality.
Grape seed extract was also shown to reduce rancid flavour development in different red meat products (eg Perumalla and Hettiarachchy, 2011; Negi, 2012).
Over the past decade, seaweed extracts have also attracted significant attention as a source of ‘natural’ bioactive compounds with valuable nutraceutical, antioxidant and antimicrobial properties, while they have also been shown to be rich in fibres and dietary iodine therefore significantly contributing to enhanced food quality.
Seaweed polysaccharides have been reported to possess biological activities of medicinal importance as well as being a source of dietary fibres and prebiotics. Some of the best known polysaccharides, namely carrageenans and alginates, have been extensively used in the food industry in the development of edible packaging material mainly for ready-to-eat products.
The high content of minerals promotes the use of seaweeds as a means of reducing the salt content in many foods, however only limited research is publicly available on the use of seaweeds and their extracts as potential food preservatives.
Factors that would need to be considered and addressed for the use of seaweeds for food applications involve their potential effects on the product’s appearance and sensory characteristics as well as the possibility of their pollution by industrial wastes and heavy metals (eg Gupta and Abu-Ghannam, 2011).
Essential oils (EOs) contain a mixture of compounds, such as terpenes, alcohols, phenols, esters, etc, and have mainly been used as food flavourings or functional ingredients. However, many also exert significant antimicrobial activities. The antimicrobial and antiviral properties of plant EOs have been shown in a number of different applications such as in raw and processed food preservation, pharmaceuticals and alternative medicine.
Tea-tree oil is an essential oil of the Australian native tree Melaleuca alternifolia. Its major constituents include a variety of terpene molecules as well as ?-pipene, 1,8-cineole and linalool and it has been identified as important antifungal agent. Other key EOs (and phenols) are thymol from thyme and oregano, cinnamaldehyde from cinnamon and eugenol from cloves.
The monoterpenes and aldehydes from essential oils are of particular interest as natural antimicrobials as they leave a minimal residue even though their volatile nature may make them difficult to apply in practise. The fresh and dried leaves of rosemary have also been very frequently used in the traditional Mediterranean cuisine as an additive.
Although they have a bitter, astringent taste, they have been extensively used in cooking. Historically, rosemary has been used as a medicinal agent to relieve symptoms caused by respiratory disorders.
Rosemary extracts are commonly used in aromatherapy to treat anxiety-related conditions. The antibacterial and anti-fungal properties of rosemary EO have been well documented making it an important natural antimicrobial candidate for the food and pharmaceutical industry (eg Jiang et al, 2011).
On many occasions, EOs and their active ingredients have proved to be less effective in food matrices; a result of the interaction of phenolic compounds with proteins, lipids and aldehydes. However, it has also been demonstrated that their combination with other antimicrobial compounds, such as bacteriocins, can deliver a significant synergistic effect of great potential against major foodborne pathogens and spoilage microorganisms (eg Turgis et al, 2012).
Vanillin (4-hydroxy-3-methoxybenzaldehyde) is the major constituent of vanilla beans and has been used as a flavouring compound in a number of different foods such as ice cream, confectionery products and beverages. It also exhibits an important antimicrobial activity, mainly against yeasts. Vanillin has been shown to be an important inhibitor of yeasts and moulds (eg Fitzgerald et al, 2003).
Herbs and spices have been used traditionally as food additives to extend the shelf life of foods and also improve their sensory characteristics. They are rich in phenolic compounds and have significant antioxidant properties. In foods, they are able to reduce lipid oxidation and can therefore improve product quality.
Numerous studies describe the antimicrobial properties of individual herbs and spices (eg thyme, cumin, sage, bay leaf etc) against a number of food-borne pathogens and spoilage microorganisms. In combination with other antimicrobial compounds they are able to exert a significant preservative effect in complex food matrices such as meat.
Tumeric and its active component curcumin have attracted additional attention as a result of their antioxidant, antimutagenic and anticancer properties as well as pharmacological activities against arthritis and indigestion (eg Negi, 2012).
The natural colours and flavours market has been experiencing a significant growth resulting in a notable increase in products claiming ‘no artificial’ or ‘natural’ colours and flavours. Natural flavours mainly derive from different parts (eg bark, peel, leaf, etc) of fruits, vegetables, spices and other plants with essential oils being the most common natural flavour complexes used in different foods.
Despite the attention to the ‘natural’ trend, the replacement of chemical ingredients (preservatives, colours or flavours) with their ‘natural’ alternatives has been technically challenging with most problems relating to the production processes and the shelf life of end-products.
Many ‘natural’ ingredients are not as pure as artificial ones, and this can significantly increase the effective levels required in a product, further impacting its physicochemical and organoleptic characteristics as well its cost. Naturally derived ingredients are generally heat sensitive and considering that most heat processing is based on pasteurisation conditions, this has turned attention to research for milder and more energy efficient processing regimes and technologies as well as intelligent packaging that is able to reduce the risk of oxidative damage, a main factor in colour and flavour degradation.
There is no doubt that the ongoing research on the identification of new ‘natural’ ingredients and evaluation of their potential applications has already boosted product and process innovation as well as of food safety and quality, and there is doubtless more to come.
Dr Evangelia Komitopoulou is the global technical manager for food at the global inspection, verification, testing and certification company, SGS, in the UK.
© FoodBev Media Ltd 2024