Abstract
Natural colorants have been used in several ways throughout human history, such as in food, dyes, pharmaceuticals, cosmetics, and many other products. The study aimed to isolate the natural colorant-producing filamentous fungi Aspergillus niger from soil and extract pigments for its potential use specially for food production. Fourteen soil samples were collected from Madhupur National Park at Madhupur Upazila in the Mymensingh district, Bangladesh. The Aspergillus niger was isolated and identified from the soil samples by following conventional mycological methods (cultural and morphological characteristics), followed by confirmatory identification by a polymerase chain reaction (PCR) of conserved sequences of ITS1 ribosomal DNA using specific oligonucleotide primers. This was followed by genus- and species-specific primers targeting Aspergillus niger with an amplicon size of 521 and 310 bp, respectively. For pigment production, a mass culture of Aspergillus niger was conducted in Sabouraud dextrose broth in shaking conditions for seven days. The biomass was subjected to extraction of the pigments following an ethanol-based extraction method and concentrated using a rotary evaporator. Aspergillus niger could be isolated from three samples. The yield of extracted brown pigment from Aspergillus niger was 0.75% (w/v). Spectroscopic analysis of the pigments was carried out using a UV–VIS spectrophotometer. An in vivo experiment was conducted with mice to assess the toxicity of the pigments. From the colorimetric and sensory evaluations, pigment-supplemented products (cookies and lemon juice) were found to be more acceptable than the control products. This could be the first attempt to use Aspergillus niger extracted pigment from soil samples in food products in Bangladesh, but for successful food production, the food colorants must be approved by a responsible authority, e.g., the FDA or the BSTI. Moreover, fungal pigments could be used in the emerging fields of the food and textile industries in Bangladesh.
Highlights
The addition of food colorants is commonly used to maintain and enhance the real color of a food substance, and sometimes to preserve it as well [1]
Potato dextrose agar (PDA) was inoculated with the inoculum prepared from 14 soil samples, and 10 samples revealed a positive based on the colonial growth of fungi after 5–7 days of incubation at 28 ± 2 ◦C
Results of Aspergillus niger Fermentation Nine days was the optimum time for the fermentation of A. niger needed to obtain a natural pigment from a liquid solution with a pH of 4.5
Summary
The addition of food colorants is commonly used to maintain and enhance the real color of a food substance, and sometimes to preserve it as well [1]. Plants are a good source of pigments, but due to some issues such as seasonal dependency, price, and variations in color intensity and hues [2], researchers and industry prefer to use microbes for pigment production This is due to the ease of large-scale production for the extraction of pigments [3], which are more cost effective and can be harvested throughout the year with no side effects, as well as being eco-friendly and biodegradable [4]. Dyes obtained from nature are eco-friendly and more degradable than other synthetic dyes [7] Because of these beneficial effects, the pharmaceutical and agrochemical industries have an interest in these secondary metabolites which include cephalosporin [8], cyclosporine [9], statin drugs [10] and, most importantly, penicillin [11]. As a means to promote the use of healthier food additives, filamentous fungi are being used under supervision in economically advanced countries as a readily available source of natural colorants [17]
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