The natural color of foods is due primarily to carotenoids, anthocyanins, betanin and chlorophylls, either as inherent food constituents or as food or feed additives. These compounds have drawn considerable attention in recent years, not because of their coloring properties, but due to their potential health-promoting effects. Their occurrence and levels in foods, along with the factors that influence the composition, have been widely investigated. Processing effects have been actively studied. In spite of the intense search for plant and microbial sources and efforts to increase yield, few natural food color additives have reached the market. Lack of stability is a major deterrent; microencapsulation and nanoencapsulation are being advocated to minimize this problem.

Natural food pigments and colorants

Background Worldwide consumers seek most delightful and appealing foodstuffs, at the same time they require safer, more nutritious and healthier products. Color is one of the most important organoleptic attributes that directly affects consumers' acceptance and food selection. Scope and approach The present report aims to provide an extensive approach to the field of food (natural/synthetic) colorants, namely those who are currently allowed with established acceptable daily intake (ADI). It also describes the biotechnological and industrial techniques that have been used to optimize food attractiveness, shelf life and color stability, as well as the general trends and future perspectives of food science and technology in the topic of food colorants. Key findings and conclusions Synthetic food colorants were largely used, but have been progressively substituted by those obtained from natural origins. Numerous side effects and toxicity, at both medium and long-terms, allergic reactions, behavioral and neurocognitive effects have been related with their use. Otherwise, naturally-derived food colorants seem to provide high quality, efficiency and organoleptic properties, and also play a contributive role as health promoters. Anthocyanins, carotenoids, phenolic compounds, beet derivatives, annatto and some curcuminoids are among the most commonly used, while strict regulatory practices have been applied looking for food quality assurance.

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Food colorants: Challenges, opportunities and current desires of agro-industries to ensure consumer expectations and regulatory practices

Ohmic heating or Joule heating has immense potential for achieving rapid and uniform heating in foods, providing microbiologically safe and high quality foods. This review discusses the technology behind ohmic heating, the current applications and thermal modeling of the process. The success of ohmic heating depends on the rate of heat generation in the system, the electrical conductivity of the food, electrical field strength, residence time and the method by which the food flows through the system. Ohmic heating is appropriate for processing of particulate and protein rich foods. A vast amount of work is still necessary to understand food properties in order to refine system design and maximize performance of this technology in the field of packaged foods and space food product development. Various economic studies will also play an important role in understanding the overall cost and viability of commercial application of this technology in food processing. Some of the demerits of the technology are also discussed.

Technology, applications and modelling of ohmic heating: a review

Anthocyanins have gathered the attention of the scientific community mostly due to their vast range of possible applications. They have been the center point of the research in many different fields, among which is food development, where their innate coloring, antioxidant capacity, and biological potential open interesting venues to the development of new food additives and functional foodstuffs. As the range of application grows, so does the necessity to obtain these compounds, and since they are naturally occurring, the most common way to obtain anthocyanins is to extract them from different plant sources, such as fruits and flowers. Several efforts have been made to develop methods that allow for better extraction yields and higher purification rates therefore this review aims to compile the information regarding extraction and purification procedures in a comprehensive manner.

Anthocyanin extraction from plant tissues: A review

Extraction of anthocyanins and polyphenols from black rice (Oryza sativa L.) by modeling and assessing their reversibility and stability.

Black glutinous rice bran (Oryza sativa L.) is a potential source of the dark purple anthocyanin pigments. This study investigated some quality aspects and bioactive compounds of the colourant powder obtained from rice bran extracted by ohmic heating (OHM) assisted solvent extraction. The moisture content (MC) of the bran was adjusted to 30% and 40%. Four different levels of electric field strengths (E) of 50, 100, 150, and 200 V cm– 1 were applied. The results showed that OHM assisted solvent extraction was a promising method offering both high yield and high concentration of bioactive compounds. The solubility, aw, bulk density, and color values (L*, C*, and h°) of the colorant powder of all treatments were comparable. The colourant powder obtained from the bran extracted using OHM with 30% MC (E=100, 150, and 200 V cm– 1) and 40% MC (E = 50, 100, 150, and  V cm– 1) had the highest level of bioactive compounds. Industrial relevance The ohmic heating was a promising technique to assist solvent extraction of anthocyanin pigment from black rice bran. The colourant powder prepared by ohmic heating assisted (CP-OHM) had higher colourant yield, anthocyanin pigments, and bioactive compounds than conventional methods. The present study suggested that ohmic heating could be applied to develop industrial production scale of natural colourants.

Ohmic heating-assisted extraction of anthocyanins from black rice bran to prepare a natural food colourant

The study of the stability of anthocyanins in food colorant powder is important to predict the quality changes occurring as the food products are processed, to prevent and control the degradation of the anthocyanins. The objectives of this study were to identify anthocyanin components in natural food colorants obtained from black rice bran, and investigate their thermal stability at 60, 80, and 100 °C, pH stability from 2.0 to 5.0 and also their correlation with visual color, L
 *, C
 *, and h°. Results showed that only six types of anthocyanins, cyanidin-3-O-glucoside, cyanidin-3-O-rutinoside, delphinidin, cyanidin, pelargonidin and malvidin were present in raw black rice bran (BRB) and black rice bran colorant powder (BCP). The thermal degradation of both the visual color and the anthocyanin content in the BCP followed a first-order kinetic reaction model. The temperature-dependent degradation was adequately fitted to the Arrhenius equation. In terms of the pH stability, increasing pH values resulted in lower activation energies (E
 a
 ) and higher half-life (t
 1/2
 ) values for both color parameters and individual anthocyanins when heating from 60 to 100 °C. Moreover, the degradation rate constant (k) increased with increasing temperature and pH value. The degradation of cyanidin-3-O-glucoside and total anthocyanins showed a strong positive correlation with C
 *. The changes in visual color may be used as an on-line quality control indicator during thermal processing of food products containing rice bran colorants which have high anthocyanin content.

Thermal and pH degradation kinetics of anthocyanins in natural food colorant prepared from black rice bran

The study aimed to investigate the effect of stabilisation using ohmic heating (OMH) on lipase activity, bioactive compounds and antioxidant activity of rice bran. The moisture content of rice bran samples was adjusted to 20, 30 and 40 %. Alternative current electricity (50Hz), with three levels of electrical field strengths (EFS) of 75,150 and 225 Vcm were applied, in order to stabilise the rice -1 bran. Lipase activity, free fatty acid (FFA), and thiobarbituric acid reactive substances (TBARS) of stabilised rice bran during storage at 4°C were investigated. The influence of OMH on the concentration of phenolic compound, a-tocopherol, a-oryzanol and the antioxidant activity of samples were also evaluated. The results indicated that OMH was an effective method for stabilisation of rice bran with moisture addition. According to this study, the EFS at 150-225 Vcm and MC of rice bran -1 30-40 % were the optimum conditions to retard the increasing of FFA content, lipase activity and lipid oxidation during storage. Moreover, the stabilised rice bran using OMH yielded the highest levels of phenolic compound, a-tocopherol, a-oryzanol, and antioxidant activity.

Effects of ohmic heating on lipase activity, bioactive compounds and antioxidant activity of rice bran.

This study determined the phytochemicals in black colorant powder (BCP) prepared from black waxy rice bran, including phenolic compounds, carotenoids, total anthocyanins, and antioxidant activity. The moisture content (MC) of the rice bran was adjusted to 30% and 40% (% wet basis). Four levels of electric field strength (E) of ohmic heating were applied to assist solvent extraction (OHM-ASE) to prepare the BCP. The steaming-assisted solvent extraction (ST-ASE) and solvent extraction (RB-SE) served as controls. BCP extraction using OHM-ASE with 30% MC (E=100, 150, and 200 V/cm) and 40% MC (E=50, 100, 150, and 200 V/cm) showed higher concentrations of gallic acid (253.29–257.57 µg/g), caffeic acid (129.34–136.12 µg/g) ferulic acid (630.74–663.34 µg/g), total phenolics (187.18–201.61 µg GAE/g), lutein (70.6–72.4 µg/g), β-carotene (4.81–5.12 µg/g), and total anthocyanins (812.17–847.09 mg/100 g) than those obtained from either ST-ASE or RB-SE. The zeaxanthin and p -coumaric acid concentrations in the BCP obtained from all OHM-ASE extracts were comparable to those from ST-ASE. In addition, the BCP extracted with OHM-ASE showed the strongest antioxidant activity of all treatments. This study demonstrated that BCP prepared from OHM-ASE can be considered as a valuable source of phytochemicals with high antioxidant properties.

Phytochemicals and antioxidant capacity of natural food colorant prepared from black waxy rice bran

In the production process of rice bran oil (RBO), the bran itself requires stabilization immediately after milling to protect against oil degradation from lipase. This study aimed to investigate the effects of stabilization and extraction methods on the chemical quality, bioactive content, and antioxidant activity of RBO. Steaming and ohmic heating (OHM) were used to stabilize rice bran before oil extraction using three extracting methods namely, immersion in n-hexane, Soxhlet, and an enzymatic method. The oil obtained from rice bran stabilized using OHM and extracted using the enzymes had the best chemical quality with the lowest values of FFA (1.51 ± 0.04%), highest level of γ-oryzanol (1190.1 ± 89.3 µg/g), and strongest total antioxidant activity (21.3 ± 0.32 mg AEE/g and 15.5 ± 0.24 mg BHAE/g). Results suggested that combination between OHM and enzymes is an effective process for the preparation of RBO and can be considered as an alternative extraction process.

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Pheeraya Chottanom

Papers

Ohmic heating-assisted extraction of anthocyanins from black rice bran to prepare a natural food colourant

Thermal and pH degradation kinetics of anthocyanins in natural food colorant prepared from black rice bran

Effects of ohmic heating on lipase activity, bioactive compounds and antioxidant activity of rice bran.

Phytochemicals and antioxidant capacity of natural food colorant prepared from black waxy rice bran

Impact of stabilization and extraction methods on chemical quality and bioactive compounds of rice bran oil.