Cite this asUdemba IO, Olasanmi B, Iluebbey P (2023) Influence of exposure to light and storage period on color changes in gari produced from bio-fortified cassava (Manihot esculenta Crantz) varieties. Glob J Ecol 8(1): 019-023. DOI: 10.17352/gje.000077
Copyright© 2023 Udemba IO, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Light degrades carotenoids and thus the color of bio-fortified gari during storage. This study was therefore conducted to evaluate the effect of exposure of bio-fortified gari to light during storage on its color. gari samples obtained from the processing of fresh storage roots of three yellow root cassava varieties (TMSI011368, TMSI010593, and TMSI010539) and a white root variety (TMS30572) as check were packaged in three replicates in transparent white plastics containers (light condition) and blue plastics containers wrapped in black polythene bags (dark condition). These were stored on an open shelf in the laboratory in a 4 × 2 × 13 factorial experiment in a randomized complete block design. Immediately after processing and monthly for 12 months, the gari samples were evaluated for color using a scale of 1 (white) to 8 (pink). The result showed that yellowness of the gari from bio-fortified cassava varieties decreased over the storage period from 5.5 (TMS010539) immediately after processing to 2.5 (TMS010593, under both storage conditions) at 12 Months After Storage (MAS). The change was significantly (p < 0.05) influenced by variety, storage duration and storage condition. gari from varieties TMSI011368 and TMSI010593 had the least (38.3%) and highest (50.2%) percentage reduction in yellowness, respectively at the end of the storage period (12 months). Across the storage period, the mean color of gari samples stored in the dark condition (3.37) was significantly higher than the mean color of gari samples exposed to light (3.22). Therefore, the proper selection of cassava variety and the use of packaging containers that screen light from bio-fortified gari during storage can best preserve its color and ensure the availability of a reasonable amount of carotenoids to consumers after long-term storage (12 months).
gari is a creamy-white, toasted, partially gelatinized, free-flowing granular flour made from cassava roots [1,2]. It has a slightly sour and acidic taste. Babatunde  reiterated that over 70% of total cassava produced in West African countries including Nigeria is processed into 7 - 10 million tonnes of gari annually. In Nigeria and many African countries, gari is eaten in different forms either as a snack or a full meal . Recently, the development of bio-fortified varieties of cassava that contain significant levels of provitamin A carotenoids had resulted in the production of bio-fortified gari with an appearance similar to gari made with palm oil [2,5]. In practice, a child who consumes 100g of bio-fortified gari daily would have his/her vitamin A daily nutritional requirements met .
The majority of gari produced by processors are rarely consumed immediately after processing but are stored. Storage of gari is also practiced at commercial and household levels. The period of storage is on average around 6 months, but some people can store for up to a year. Storage conditions of food products had been reported to determine the final characteristics and composition of the food product . Globally, major and minor carotenoid compounds degrade during storage at ambient temperature. Also, the vitamin A activity of bio-fortified cassava products decreases sharply during storage [7,8]. Since carotenoid pigments in food are denoted by varying shades of color yellow , degradation of carotenoid in food results in a reduction of food yellowness and loss of nutritional values . Moreover, a strong and positive correlation between the intensity of the yellow color of cassava root and its total carotenoid content had been established by several authors [2,11-13]. Njenga, et al.  reiterated that 98% of the variability in the carotene content of cassava can be explained by the variability in root color. This is the sequel to the fact that the extent of the pigmentation of the parenchyma of cassava root is closely linked to its carotenoid content .
Uchechukwu-Agua, et al.  noted that color variation (and subsequently carotenoid variation) observed during the storage of cassava products can be accredited to the length of storage and cultivar differences. Also, the stability of carotenoids present in food products had been demonstrated to be influenced by factors such as the presence of oxygen, exposure to light and heat, type of food matrix as well as the type and physical form of carotenoid compounds [16-18]. The carotenoids in dehydrated foods like gari are most likely to undergo degradation during storage because of their great surface area and porosity which increases their exposure to oxygen and light . Understanding how carotenoids (which can be depicted by the yellow color) of bio-fortified gari degrade during storage is critical because it will affect its nutritional impact. This knowledge can help processors, sellers, and consumers of bio-fortified gari adjust their storage methodology for enhanced carotenoid preservation. Hence, this study was conducted to determine the effect of light and darkness on the color of bio-fortified gari during long-term storage.
The result presented in Table 1 shows that varietal, storage condition, storage duration, and interaction of variety × storage condition × season; storage duration × storage condition × season effects were significant for the color of gari in this study. The yellow color of all the bio-fortified gari samples decreased with increase in storage duration across the two storage conditions while the color of gari from white root increased (Figures 2 and 3). There was no significant difference in color scores of gari from the three bio-fortified yellow root cassava varieties at each storage duration under both daylight and dark conditions. However, the color of the bio-fortified gari changed from a score of 5.5 (TMSI010539) at 0 months after storage (MAS) to 2.5 (TMSI010593, under both light and dark conditions) at 12 MAS (Figures 2 and 3). During storage, variation in the color of gari from the white variety ranged from 1.7 (0 MAS) to 2.0 (under both storage conditions) at 12 MAS (Figures 2 and 3). An appraisal of the trend of color changes showed that the decrease in the yellow color of gari from the initial (immediately after processing) (4.38) till one month (4.27) in storage was not significant (Table 2). Subsequently, a significant difference was observed in a decrease of yellow color intensity of the stored gari samples across all months of storage except from 4 (3.46) to 6 (3.33) months; between 8 (2.88) and 9 (2.77) and 11 (2.52) and 12 (2.44) months of storage (Table 2). The mean color score of gari samples stored under dark condition (3.37) was significantly higher than the value recorded for samples exposed to light (3.22) over the storage period (Table 3). Towards the end of storage (12 MAS) bio-fortified gari from TMSI011368 and TMSI010593 stored under dark conditions attained stability in carotenoids content (depletion of the color of gari stopped) at 9 and 10 MAS, respectively (Figure 4). gari samples from these two varieties exposed to light attained stability at 11 MAS (Figure 4). Notably, gari from TMSI011368 had the highest carotenoid content (depicted by the highest color of 2.8) at stability (towards the end of storage) in both storage conditions, though it had the least yellowness score immediately after processing (4.7) among the bio-fortified yellow gari (Figure 4). Carotenoids in gari from variety TMSI010539 became stable at 11 MAS in both storage conditions (Figure 3). Percentage change in color intensity of the gari samples after 12 months of storage followed the order of TMSI010593 (50.22%) > TMSI010539 (50.04%) > TMSI011368 (38.25%) > TMSI030572 (19%) (Table 4).
Carotenoids are denoted with yellow or orange pigments which contribute to the yellow color of bio-fortified yellow gari . The observed decrease in yellowness of bio-fortified gari samples (stored in both storage conditions) with an increase in storage duration corroborates the earlier findings of Olasanmi, et al.  who observed a progressive decrease in yellowness of bio-fortified gari samples exposed to light during storage. Also, Uchechukwu-Agua, et al.  reiterated that oxidation, degradation of yellow pigment of bio-fortified cassava product, and length of storage were responsible for the decline of its yellowness. Carotenoid degradation (depicted by yellow color degradation) is an oxidative process that is not interrupted during storage . This is due to the double bond in the carotenoid carbon chain which makes them susceptible to chemical reactions induced by oxygen, light, and heat during processing or storage [25,26]. Thus, increase in storage duration led to augmented degradation of yellow pigment (contained in the gari samples) and consequently decrease in yellowness of gari. Degradation of carotenoids content during storage is a major challenge in maintaining the health benefit of high carotenoid products . The present finding of an increase in the color of gari from white root during storage agrees with the earlier submission of Uchechukwu-Agua, et al. , who reported similar observations from the storage of flour from white root cassava variety and attributed the increase in color score to the effect of oxidation during storage. The record of lower color retention for gari samples stored under light condition highlights the effect of the permeability of packaging material to light on the quality of stored products as observed by Olasanmi, et al. . Exposure of food products to light during storage had been reported to have a detrimental effect on food quality . Specifically, reports in the literature indicated that the decline in the carotene content of some stored food products can be accounted for by exposure to light [2,29,30]. Conversely, the dark condition created a better barrier to light penetration which resulted in higher color retention in bio-fortified gari. Howbeit, the observation of a yellow color decline in gari samples stored under dark conditions confirms the earlier findings of Oliveira, et al.  and Osagie, et al.  who observed continuous degradation of carotenoids of some bio-fortified cassava products during storage in the absence of light. This can be attributed to the auto-oxidation of anthocyanin and β-carotene in the bio-fortified products as opined by Kaur, et al. .
The finding of no significant seasonal variation in the color of the gari over the storage period suggests that changes in the color of the gari in the two seasons of evaluation followed the same trend. The observation of significant effect of variety on the color of gari is consistent with the separate submissions of Chavez, et al. ; Oliveira, et al.  and Olasanmi, et al.  who reported a significant varietal influence on color and carotenoid content of stored bio-fortified cassava products including gari. However, the absence of significant difference in the color of the three bio-fortified gari samples at each storage duration, suggests that changes in carotenoid content of the bio-fortified gari samples at each duration of storage were comparable. The low pigment color of gari from the white root check variety throughout the period of this study indicates that bio-fortified gari can still supply some reasonable quantity of carotenoid even after long-term storage and thus a good panacea for vitamin A deficiency when consumed. After 12 months of storage, the record of highest and least percentage color reduction from gari of varieties TMSI010593 and TMSI011368, respectively (among the bio-fortified gari samples) implies that degradation of carotenoid pigment was fastest in gari samples from variety IITA-TMSI010593 and least in TMSI011368. This connotes better stability of carotenoid in gari from variety TMSI011368 among the bio-fortified gari samples and better nutritional composition for end users after long-term storage. This finding affirms the observation of Olasanmi, et al.  from a separate study who noted that gari samples from cassava variety TMSI011368 had the highest color retention after 1year storage period for two seasons when compared to gari samples from other varieties. This observation of best color retention in gari of variety TMSI011368 which had the lowest initial color score after processing (among the yellow gari) suggests that carotenoid retention capacity (depicted by yellow color intensity) of gari is not a function of the initial carotenoid content but the inherent carotenoid stability property of the cassava variety.
Degradation of carotenoids (depicted by fading of yellow color) during food storage limits the optimization of nutritional benefit of bio-fortified cassava products. Based on the outcome of this study, it can be concluded that the color of bio-fortified gari can be significantly influenced by cassava variety and storage condition and duration. Although a decline in yellowness of bio-fortified gari was observed under both light and dark conditions, the achievement of better color preservation under the dark condition makes it a better option for long term storage of bio-fortified gari obtained from yellow root cassava varieties with high carotenoid stability during storage.
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