Grain color measurement and nutrient content of local pigmented rice from South Sulawesi

This study is aimed at measuring the color and nutrient contents of local pigmented rice from South Sulawesi. Five grams of husked rice grains are placed on a 60 mm petri dish before attaching the TES 135 colorimeter. Total protein content was measured using the Kjeldahl method. Total fat content was measured using Soxhlet. Selected varieties were analyzed further for zinc (Zn) and iron (Fe) content using Atomic Absorption. Spectroscopy. Data were analyzed using a one-way ANOVA, followed by the Duncan Multiple Range Test at 5%. The results showed that the Le’leng variety showed the lowest values of L*, a*, and b*, which means that it has the darkest color. The highest protein content is found in Le’leng and Kobo. The protein content of local pigmented rice is higher but tends to be similar in fat content to modern rice. It can be concluded that colorimetry grain color measurement follows the grains’ visual appearance. The darker the grain color, the lower the L*, a*, and b* parameters. Local pigmented rice from South Sulawesi has significant protein, fat, Fe, and Zn. Color appearance can be a preliminary visual indicator of the bioavailability of compounds with health benefits in pigmented rice..


Introduction
In addition to white rice, there are assorted colors of rice grains called pigmented rice.Indonesia has a diversity of pigmented rice that are dominated by traditional varieties.Traditional varieties refer to local varieties or landraces cultivated by farmers for generations.Grain coloration comes from the pigment content in the endosperm aleurone, which can be red, dark purple, to black color.The intensity of color in pigment rice can be diverse.Color density is suspected to be related to anthocyanin levels in seeds.Anthocyanin compounds are the pigmented flavonoids that give some rice varieties their purple pericarp [1].Local varieties are known to be high in dietary fiber, resistant starch, minerals, carotenoids, flavonoids, and polyphenols, thus, eating local pigmented rice helps to improve human health by 1230 (2023) 012057 IOP Publishing doi:10.1088/1755-1315/1230/1/012057 2 lowering the incidence of silent diseases [2].Pigmented rice is high in antioxidants,macronutrients, and micronutrients [3].Purple rice has a wide range of nutrients, like K, Fe, Zn, Cu, Mg, Mn, and P, found in grains [4].
Color parameter is mainly caused by natural pigments found in different amounts in cereals and cereal products.The amount depends on their botanical origin, growing conditions, location in thekernel, and technological processes.Chemical extraction methods are usually not used to measurecolor in the food industry.Instead, automatic instruments that are quick and safe are used [5], such as colorimeter measurement.A colorimeter was used to measure the color of both raw and cookedrice, which is a crucial sense property [6].
Color measurement is critical for evaluating grain and grain products since it significantly impacts end-product quality.Colorimeters are used by grain processors and plant breeding programs to measure L*a*b* values as defined by the Commission International de L'Eclairage (CIE) in order to quantify color scientifically [7].
Rice germplasm from different countries has been found to have a wide range of anthocyanin levels in the grains [7,8].The total amount of anthocyanins in seventeen different kindsof traditional colored rice of South Sulawesi ranged from 2.89 mg CGE/100-gram dry weight to 187.23 mg CGE/100 g dry weight [8].It has been demonstrated that the nutritional quality of grainproduced by certain traditional landraces is superior to that of grain produced by conventional, modern rice varieties, primarily as a result of their more efficient accumulation of bioactive compounds [9,10] Color variation in pigmented rice was previously studied by [11] in Yogyakarta and [12] in South Sulawesi.They reported variations in colorimetric measurement.Unfortunately, the local name of most pigmented rice was not described further.Since the magnitude of anthocyanin content may contribute to the color and the antioxidant activity found in each cultivar.Therefore, variations in type group (varieties), color, anthocyanin, and othernutrients may affect understanding of various pigmented rice germplasm and their potential use.
The quantification of color intensity and nutrient content in local pigmented rice are beneficial in providing information on the germplasm's characteristics.The genetic pool of local pigmented rice might benefit future breeding programs.Information from this study can help local farmers and consumers decide which rice to grow or buy based on their preferences.Thus, this paper aims to quantify the color measurement of local pigmented rice of South Sulawesi using colorimeter and quantify the protein, fat, zinc and iron content of the grains.

Methods
The study was conducted in March-May 2019.Analysis of protein, fat, Zn and Fe content was held in the Biochemistry Laboratory of Hasanuddin University.Seven local pigmented rice from South Sulawesi and one modern red rice used in this study are listed in Table 1.The samples were harvested from the rice fields of different regions according to their habitats during the harvest period of December 2018 -March 2019.The rice grains used as samples were obtained from the threshed rice panicles and separated from the grain using a rice husker (Kett TR-130).Using a portable rice husker maintains the epidermis or the outermost part of the rice grains.
Five grams of husked rice grains are placed on a petri dish with a diameter of 60 mm on a flat surface.Attaching the TES 135 colorimeter to the samples enabled the measurement of color intensity.It generated three color parameters, namely brightness(L*), redness (a*), and yellowness (b*).Total protein content was measured using the Kjeldahl method.Total fat content was measured using Soxhlet.Selected varieties were analyzed further for micromineral of zinc (Zn) andiron (Fe) content.Collected data were analyzed using analysis of variance, followed by Duncan Multiple Range Test.

Grain color measurement
Colorimetry measurement on rice grain color showed the significant effect of variety on three color parameters (L*, a*, and b*).The lowest value of L* was found in the Le'leng variety (14.91) and significantly differed from others (Table 2).The finding is in line with the visual appearance of the grain (i.e., Le'leng has the darkest grain color in the black rice group).On the other hand, the Ambo variety has a high value for L* (38.13).This value was the highest among the black rice group and as high as the red rice variety.The highest red or green value (a*) was found in the Mandoti variety (20.47) but not significantly different from Bakka Eja (17.87) and Inpari 24 (15.73).All of them belong to the red rice group.The lowest a* value was found in the Le'leng variety (-1.53), which does not differ from Kobo and Lallodo.Le'leng and Lallodo have the lowest value for the b* parameter.Meanwhile, Mandotiand Bakka Eja has the highest blue/yellow value (b*).
In general, the result showed that black rice varieties (except Ambo) were low in the value of colorimetry measurement.The results make sense and are compatible with our expectations since Le'leng, Lallodo and Kobo appear dark grain color.Meanwhile, for Ambo variety, it has a whitish gradient in the grain color.The correlation between grain color and anthocyanin content was reported: the higher the value of the color parameters L*, a*, and b*, the lower the total anthocyanin content, and vice versa, the lower the value of the color parameters L*,a*, and b* the higher the total anthocyanin content.This finding is understandable because the higher the L* value, the lighter the color [13].Previous work of [8] also mentioned that anthocyanin was superior in the dark bold color of grains.At the same time, Ambo has black yet sheer in color.These findings also noted that the value of L*, a* and b* parameters in modern red rice was comparable to traditional red rice.Red rice was reported to be low in anthocyanin and flavonoid but highin phenolic content [8].The result of this study confirmed the potential use of color parameters as useful indicators in the selection of breeding or consumer consideration in buying.

Nutrient content
Though rice is consumed as the main carbohydrate source, the proximate analysis focuses on protein and fat contents due to their importance for the additional value.Fat functions as a energy source, dissolves vitamins so that the intestines can absorb them and prolongs satiety.Protein functions as growth and maintenance, the formation of essential bonds of the body, regulateswater balance, maintains the body's neutrality, forms antibodies, and transports nutrients and energy sources [14].Results showed the range of protein content was from 7.96 (Inpari 24) -13.65 (Le'leng).Thehighest protein was extracted from Le'leng, Kobo, Lallodo and Mandoti.The range of total fat content was 1.22 (Lallodo)-1.71(Bakka Eja).Bakka Eja, Mandoti, and Inpari 24's total fat content were the highest among the tested varieties.Ambo has 9.70% of total protein and 1.25% of fat.This result differs from [14], which previously reported that Ambo black rice from Toraja contains 1.04% protein and 1.9% fat.The protein content of Mandoti in this study (11.67) was also higher than what was reported by [ [15], which only 8.89%.The protein content of some red rice varieties in Thailand, Sri Lanka and Chinaregions varying from 7.16% to 10.36% [16].
The protein content in rice affects the texture of rice [17].Rice with high protein content produces rice that tends to be hard.In addition, proteins together gelatinization temperature affectsthe cooking time.Rice with a higher protein content requires more water and a longer cooking time.The protein content of rice is in the range of 7% [18].Rice with a protein content smaller than 8.5% tends to be fluffy.
According to the above statement, regarding our finding, only Inpari 24 has a fluffy character,since other varieties have >8.5% of protein content.Our findings are in line with those found in [19].The protein content of traditional varieties of Melik rice from Bantul, Cempo ireng rice from Sleman, Wulung rice from Banjarnegara, and other black rice bought from Beringharjo traditionalmarket varying from 8.40 -10.44%, the fat content ranged from 2.33 -2.88%.
Further assessment on the micromineral of rice grain was narrowed on selected varieties for zinc (Zn) and iron (Fe) content.Rice plant breeding can also be directed to obtain varieties with a high content of Fe and Zn.Strong synergy indicates that the assembly of plant varieties that have high Fe and Zn levels will be more effective in overcoming anemia [20].This program requires the availability of germplasm with adequate genetic diversity for the character to be improved (which is rich in Fe and Zn) for breeding.Rice with high Fe and Zn contents is expected to be an approach to nutritional interventions for rice consumers [21].The Fe content of local rice in Indonesia is lower (11.28 ppm) than in IRRI (13.2 ppm).In contrast, the average Zn content is higher (31.37 ppm) than local rice in IRRI (24.2 ppm) [22].
Our finding found the highest zinc content in the Kobo variety (37.60ppm).Interestingly the finding founds that Le'leng (26.47 ppm) has zinc content as low as Mandoti (27.13 ppm) (Table 4).Though Kobo and Le'leng are black rice, they are different in rice type.Kobo is a non-waxy black rice, while Le'leng is a waxy one.It may be challenging to determine if thewaxy trait is responsible for the level of zinc content due to limited data on our treatment and sample.Based on its varietal description, Inpari IR Nutri zinc possesses a Zn content of as much as 34.51 ppm.At the same time, other varieties, such as Ciherang, contain 24.06 ppm [23].The content of Fe ranged from 20.88 (Mandoti) to -34.84 ppm (Kobo).Le'leng also had the same level of content Fe as Kobo.This finding aligns with a previous study that reported the Fe content of some black rice varieties from Java island ranged from 16,09-34,09 ppm [19].Wetland conditions were found to be more conducive to intense pigmentation in the production ofpurple rice, as well as higher Zn and Fe concentrations [24].Iron is essential for making healthy red blood cells, using energy, and digesting food [25].

Conclusion
The darker the grain color, the lower L*, a*, and b* parameters of colorimetric measurement.Le'leng variety has the darkest grain color and the lowest L*, a*, and b*.It also contains the highest protein.In general, the protein content of local pigmented rice was higher than the modern variety (Inpari 24).Regarding Fe and Zn content, the Kobo variety has the highest amount.Rice grains with dark color can be an initial indicator of the bioavailability of bioactive compounds.

Table 1 .
Material of the study

Table 2 .
Grain color measurement of pigmented rice using a colorimeter.The mean followed by the same letter or letters within the column are not significantly different according to Duncan Multiple Range Test at the 0.05 significance level

Table 3 .
Proximate analysis for total protein and fat content

Table 4 .
Fe and Zn content of selected pigmented riceThe mean followed by the same letter or letters within the column are not significantly different according to Duncan Multiple Range Test at the 0.05 significance level.1230 (2023) 012057