Food additives: production of microbial pigments and their antioxidant properties
Introduction
US FDA states that “any substance that is reasonably expected to become a component of food is a food additive that is subject to premarket approval by FDA”. Microorganisms and plants produce certain substances which exhibit different colors due to selective color absorption; these substances are termed as pigments. These pigments are extracted and utilized in pharmaceutical industry, textile and dyeing industry, food & dairy industry and cosmetics industry [1••, 2, 3••, 4, 5••, 6••, 7]. Naturally occurring pigments like isoprenoids, alkaloids and flavonoids, have been used for fragrance, flavor and color in various food types since prehistoric times [1••, 8, 9, 10]. According to various studies conducted recently it is well evident that pigments extracted from microbes are beneficial over synthetic pigments and pigments that are extracted from plants owing to their stability, availability due to no seasonal variations, cost-effectiveness, high yield through strain improvement [5••, 6••, 11] and smooth downstream processing for extraction [12]. Also, there exists a recent trend of public awareness on adopting environmental friendly and human safety measures [13]. Consumers have developed aversion toward application of synthetic food colorants; therefore natural food colorants are in huge demand [14, 15].
In past various research studies have been conducted to explore the existence of diverse coloring pigments in plants and microbes [4, 11, 16]. Microbial strains producing pigments can be isolated, extracted, characterized and purified from different environmental sources like — soil, water, plants and animals [17, 18]. Recent research studies indicate the immense potential of microbial pigments in the food industry and possibility of discovering novel strains from various unexplored sources like agro industrial waste, marine fungi, and filamentous fungi etc. [19, 20•, 21, 22].
Recent review study states that currently there are almost 2500 types of food additives being used globally and US FDA lists around 3000 ingredients in the food additive database [23]. It also states that almost 200 thousand tones of food additive are being used per year; which highlights the fact that western diet consists of approximately 75% of the processed food. Each person's average annual intake of food additives is estimated to be 3.6–4.5 kg [23].
Food items that are rich in nutrients, flavor, aroma and texture cannot be consumed unless the color exhibited makes its appearance relishing. Worldwide consumers are fond of colorful food products and food dishes [3••, 24]. Microbial pigments not only add color to food, they also have populous medicinal properties like antioxidant, antimicrobial, anticancer, immunoregulation, anti-inflammatory, antiproliferative, and immunosuppressive etc. [1••, 3••, 25]. Most commonly used food grade pigments are β-carotene, arpink red, riboflavin, lycopene and Monascus pigments [1••, 3••, 12].
The production of many currently authorized natural food colorants has a number of disadvantages, including a dependence on the supply of raw materials and variations in pigment extraction. Currently, fermentative large scale production of natural food colorants is feasible in the global market [69]. Maximization of the pigment yield while minimizing the production costs has been the attention of current techniques applied to manufacture microbial pigments at large-scale. It has also been reported that process optimization techniques have deployed statistical experimental designs and response surface analysis along with limited use of artificial intelligence like genetic algorithms [52]. Potential of renewable sources like fruits, vegetables, lichens, and marine life etc. for novel commercial food colorants is questionable with respect to raw material's availability and high investments which are recurring. Commercial production of microbial pigments for application in food industry has been attained as a result of variety of techniques combined together, namely — fermentation techniques (solid or submerged state), chemical modifications, production using agro-industrial wastes, genetic modification techniques etc. [56, 71••, 82]. Previous research studies demonstrate that commercial production of microbial pigments remains to be in the research and development stage [3••].
Current literature review article elucidates the current scenario of microbial pigments as food colorants and underlines the importance of investigating large scale production strategies for microbial pigments, novel strains of microbes producing colored pigments and techniques aiding in high yield-extraction of colored pigments using microorganisms.
Section snippets
Why microbial pigments as food additive?
Consumers’ ability to differentiate between the benefits of microbial pigments and hazardous effects of synthetic pigments has greatly boosted the application of microbial pigments as food additive. According to current trends consumers’ tendency to interpret utilization of synthetic pigments as mere contaminants has been augmented [26]. Robust development and advances in technology and genetic engineering techniques have enabled food industry to produce microbial pigments [27, 28, 29, 30];
Food colorants and global market
Food colorant industry market has been noted to grow at the rate of 10–15% annually. A research report published by Leatherhead Food International (LFI) (www.leatherheadfood.com) states that by 2015 the global market for food grade pigment is expected to rise by 10% to be $1.6 billion USD [70•]. As per the current legislation by European Union 43 colorants are approved and permitted as food additives and approximately 30 additives are approved in the United States; 6 colorants amongst these 30
Microbial pigments production technologies and challenges
Algae, fungi and various types of bacteria have been used as source for commercial production of microbial pigments to be used as food additives and colorants [2, 8, 10, 15, 40, 55]. Extraction of colored pigments plays pivotal role in production at industrial level [70•]. Several research studies have demonstrated that an ideal microbe producing pigment is the one which has the ability to utilize wide range of carbon and nitrogen sources and is tolerant to temperature pH and minerals and it
Current technologies for microbial pigment production
Pigment production using microbes is highly controlled by the composition of the medium, supplemented-stimulators and optimization of culture conditions performed using experimental designs through statistics, aid in developing successful large scale production [71••].
Response surface methodology (RSM), artificial neural networks (ANN) are two of such techniques applied for microbial pigment production. In order to investigate the possible effects of medium components on pigment production a
Challenges
Extraction of highly concentrated form of pigments in a purified state remains to be a challenge for the manufacturers [6••]. Microbial pigments are usually extracellular or intracellular; extraction and purification of pigments produced intracellularly adds the stage of cell disruption and increases the downstream processing times. Stability of microbial pigments under environmental stress or when they are exposed to UV leads to degradation of the pigments [60]. Large scale commercial
Major microbial pigments in food industry
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β-Carotene
Carotenoids range from yellow to orange-red colored pigments. Microorganisms like Serratia, Micrococcus, Mycobacterium, Agrobacterium, Sulfolobus and Streptomyces [1••, 12, 61]. It is a recent trend to utilize the agro-industrial byproducts, such as cheese whey, sugarcane molasses, glucose syrup, peat hydrolysate, cellobiose and beet molasses [6••] as nutrients for producing carotenoids. β-Carotene is an antioxidant and has positive effects against few diseases. According to a current
Antioxidant properties of microbial pigments and their benefits
The unique characteristic of an antioxidant is to trap the free radicals [25]; they quench the photo sensitizer, interact with oxygen singlet and scavenges the peroxy radicals [66]. Most of the chronic diseases like cancer, diabetes, cardiovascular and autoimmune disorders are associated with the presence of free radicals [25]. Microbial pigments are potential antioxidants which when added in food products, exhibited positive effects. Carotenoids, napthaquinone and violacein have demonstrated
Novel sources for microbial pigments
Novel strains like Enterococcus hirae, Acinetobacter mufti, Pseudomonas aeruginosa were isolated from soil and cultured on brain heart infusion agar and further investigated in vitro for colored pigments and antioxidant activity was tested using DPPH assay which revealed the presence of 54.7% antioxidants; these pigments produced in laboratory have potential to be used as food colorants [22]. A recent research study has revealed the potential in filamentous fungi to produce polyketide-Monascus
Future perspectives and conclusion
Consumers’ sensitivity toward application of synthetic additives in food has led to rapid development and large scale production of natural pigments/colorants. Majority of natural food additives are derived from microbes (bacteria, fungi, yeast etc.). Exploitation of microbes for commercial production is the most focus point in development of novel food additives. There is an urgent need for development of novel strains capable of high yield of pigments using a cheap substrate with less
References and recommended reading
Papers of particular interest, published within the period of review, have been highlighted as:
• of special interest
•• of outstanding interest
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