Elsevier

Food Chemistry

Volume 278, 25 April 2019, Pages 773-779
Food Chemistry

Kinetics of β-carotene degradation under different storage conditions in transgenic Golden Rice® lines

https://doi.org/10.1016/j.foodchem.2018.11.121Get rights and content

Highlights

  • Genetic constitution of the rice variety and transgene position influenced β-carotene accumulation.

  • Vacuum packaging enhances the storage stability of β-carotene in Golden Rice®.

  • The β-carotene deterioration was faster when rice was stored after polishing.

  • Oxidative deterioration of β-carotene is higher followed by thermal deterioration.

Abstract

The effect of vacuum packing and ambient storage conditions on the stability of the β-carotene in the transgenic Golden Rice® lines was studied. The β-carotene was quantified using RP-HPLC at bimonthly intervals for a period of six months. The β-carotene concentration in the genotypes analyzed ranged from 7.13 to 22.81 µg/g of endosperm. The transgene being the same in all the genotypes, variation in the β-carotene concentration reflects on the genetic background of the rice variety and the transgene position that governed the differential accumulation of β-carotene. It was observed that in the absence of light, oxidative degradation is higher followed by thermal degradation. Weibull model with higher R2 best explained the degradation kinetics of β-carotene in Golden Rice® lines across all the storage conditions. The knowledge generated through this study can be utilized in devising an effective delivery system for Golden Rice® to the consumer.

Introduction

Carotenoids are universal pigments that impart orange, yellow and red colors naturally found in vegetables, fruits and flowers of plants and flesh and feather color of some fish and birds (Boon, Mcclements, Weiss, & Decker, 2010). The extreme hydrophobicity of the compounds restricts them to the core membranes and other hydrophobic locations where they act as antioxidants and protect the tissue from damage by free radicals. In plants, they are essential for the photosynthesis, development, root-mycorrhizal interactions and the production of plant growth regulators, such as abscisic acid, brassinosteroids, and strigolactone. Animals and humans are incapable of synthesizing the carotenoids and depend for their dietary intake on plant products. Alpha-carotene, β-carotene, β-cryptoxanthin, zeaxanthin and lutein, are the common dietary carotenoids well known for their beneficial health effects. Beta-carotene (C40H56) is the major carotenoid with provitamin A activity followed by α-carotene and β-cryptoxanthin. The vitamin A equivalency ratio of β-carotene as defined by the amount of dietary β-carotene that is equivalent to a unit amount of retinol (vitamin A) ranges from 3.8:1 to 28:1 depending on the food matrix (Giuliano, 2017, Tang, 2010). The dietary carotenoids are cleaved into provitamin A precursors and are essential in maintaining human health through promoting antioxidant activity, limiting macular degeneration of the eye upon aging, photoprotection as well as visual tuning of the eye, yolk nourishment to embryos and promoting the production of immunostimulants (Johnson, 2002, Krinsky and Jhonson, 2005).

Rice is the staple food crop providing almost 50% of the dietary caloric requirement for more than half of the world population. The poorer sections of the population in the developing nations are heavily dependent on rice for their caloric requirement. Rice is generally consumed after removing the bran layer through the process of polishing. The polished rice has poor micro-nutrient status and completely devoid of provitamin A carotenoids making vitamin A deficiency (VAD) more prevalent among the rice eaters. As no known cultivar of rice is capable of synthesizing and accumulating provitamin A carotenoids in the endosperm, a transgenic approach was adopted to introduce β-carotene biosynthesis pathway in rice endosperm and transgenic lines bearing golden yellow color seeds were named as Golden Rice® (Beyer et al., 2002). The first set of Golden Rice® lines were developed by expressing two genes viz. phytoene synthase (Psy) from the ornamental flowering plant daffodil (Narcissus pseudonarcissus) and carotene desaturase (CrtI) from the bacteria Erwinia uredevora in rice endosperm and these lines named as first generation Golden Rice® lines (GR1 series) were capable of accumulating about 6 µg/g of total carotenoids in the endosperm. Replacing the daffodil Psy, with the Psy from maize (Zea mays) improved the carotenoid content to 11.4–37 μg/g of endosperm (Paine et al., 2005). The transgenic events carrying ZmPsy were named as second generation Golden Rice® lines (GR2 series). Six events of GR2 series were made available for public sector breeding programmes by the Humanitarian Board on Golden Rice® (HumBo). Under the Indian Golden Rice® network programme, GR2R1 event was used as a donor for the introgression of provitamin A trait into the popular Indica cultivar Swarna, at Indian Agricultural Research Institute (IARI) and the advance generation backcross-derived lines bearing provitamin A trait were developed (Bollinedi et al., 2017, Bollineni et al., 2014).

Globally rice is harvested during a limited period of time but consumed all around the year. In countries like India, much of the harvest is procured by Food Corporation of India (FCI) for supply to the poorer sections of the population through the Public Distribution System (PDS). Buffer stocks of the procured cereals are maintained by storing them in large godowns and silos, where they are dried and fumigated to control storage pests. In spite of this, high temperature, humidity and strong light in the storage godowns foster pronounced chemical changes in the produce. The characteristic conjugated polyene chain of carotenoids makes them more susceptible to degradation by several agents that include light, heat, singlet oxygen and enzymes like lipoxygenase mediated oxidation. Although some literature is available on the factors influencing carotenoid degradation in cereals, there is no information on the behavior of these factors in Golden Rice® during storage. The present study was therefore attempted to understand and quantify the effect of different storage conditions on the stability of β-carotene in Golden Rice®.

Section snippets

Material

The seed samples of two events of Golden Rice® viz. GR2-R1 and GR2-E1 used in the study were obtained from Syngenta through HumBo under the license agreement with the Department of Biotechnology, Government of India. These E-events were in the background of American long grain rice variety Kaybonnet and carried carotenogenic transgenes, ZmPsy from maize and CrtI from the bacterium Erwinia uredevora, both driven by endosperm-specific glutelin 1 (Gt1) promoter of rice, while the selectable marker

Statistical analyses

The β-carotene concentration of the samples was given as mean ± standard deviation (SD). Factorial analysis of variance (ANOVA) was performed in Minitab V18 to determine the effect of genotype, rice type, storage condition and storage duration on β-carotene degradation. Degradation kinetics of β-carotene was modeled hypothesizing first-order kinetics and Weibull distribution model (Jiang, Zheng, & Lu, 2014). First order reaction constants for β-carotene degradation in Golden Rice® were obtained

The β-carotene concentration of Golden rice® genotypes

Table 1 shows the β-carotene concentration of the genotypes analyzed in the study. Between the two events viz. GR2-R1 (transgene located in chromosome 1) and GR2-E1 (transgene located in chromosome 3), GR2-R1 (15.39 µg/g of endosperm) event posses double the concentration of β-carotene than GR2-E1 (7.13 µg/g of endosperm) event. The transgene construct being the same in both the E-events, the difference in β-carotene concentration between the E-events reflects on the position effect of the

Conclusion

The study delineated the importance of genetic constitution of the rice variety and the position of the transgene on the accumulation of β-carotene in the rice endosperm as well as its retention upon storage and emphasizes on the necessity of identification of the best genetic background to realize the complete potential of Golden Rice® in the alleviation of VAD. Differential water uptake during cooking by different rice varieties would influence the extent of cooking losses of β-carotene.

Conflict of interest

None.

Declaration of interests

The authors declare that they have no known competing financial interests or personal relationships.

Acknowledgments

The research work was initiated under the project titled “Development of Pro-vitamin A rich indica rice varieties through marker assisted backcross breeding using high carotenoid Golden Rice as donor” funded by the Department of Biotechnology, Government of India, New Delhi and was continued under the project “Consortium Research Platform- Biofortification” funded by Indian Council of Agricultural Research (ICAR). We thankfully acknowledge the support of both the funding agencies. The study is

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