The phytic acid phosphorus and the phenol content of brown rice and products are presented in Table 1. The content of ash and the important minerals are presented in Table 2.
The phytic acid P
The phytic acid P content of brown form of specialty rice were found to be lower than the values (5.61-9.12 g/kg or 561- 912 mg/100 g) reported for some selected rice varieties.
The phytic acid P content of different products and their intermittent forms varied from 92.74 mg/100 g-313.33 mg/100 g, the lowest was observed in
bhoja bora and the highest in intermittent form 2.
Bagchi et al., (2016) reported that the phytic acid content of raw rice and their respective popped rice of some Indian rice cultivars ranged between 0.15%- 0.27% or 150- 270 mg/100 g and between 0.18%-0.8% or 180-800 mg/100 g, respectively. They stated that higher phytic acid observed in popped rice than their respective raw form was due to disintegration of starch and higher exposer of phytic acid to extraction medium. The observed difference of our observation with that of
Bagchi et al., (2016) might be due to differences in processing as in the present study, all products involved wet processing, instead of dry processing required for popped rice. During wet processing, some of the phytic acids was lost; as the water where paddy was soaked, was discarded.
Soaking appeared to be most effective in decreasing phytic acid content. It activates the endogenous phytase enzyme that hydrolyses phytic acid to free myo-inositol and inorganic phosphate
(Kumar et al., 2017). Decrease in phytic acid P due to heat treatment was also reported (
Mahgoub and Eihag, 1998). In the present study also, phytic acid P content were decreased in almost all the specialty rice products than their respective raw forms. However, the observed increase in
sandah guri than the same in
komal chaul might be due to changes in percentage, not actual increase, as
sandah guri was made from
komal chaul by grinding and discarding the granules which did not pass through 50 micron sieve.
In the brown form of specialty rice, the phytic acid P content as percentage of total P was found to be 69.95- 88.94%; the lowest was in
bakul bora and the highest in
ronga chakua. It was reported that phytic acid P accounts for 50-80% of the total phosphorus in different cereals (
Mahesh et al.2015)
The phytic acid P content as percentage of total P of different products and their intermittent forms was found to be 37.06-88.72%, the lowest was in
bhoja bora and the highest in
korai.
It was observed that during processing of
bhaja bora from raw
michi bora, the highest amount (total 66.23%) phytic acid P was reduced. Though, decrease in the P content during the processing of the same was 25.81% only. It reflects that part of the P attributed by the degradation of phytic acid during heating are retained in the products analyzed in the present study, including
bhaja bora. However, the observed decrease of total P during soaking was the loss probably due to water soluble nature of phytic acid.
The total phenol content
The total phenol content of brown form of specialty rice was found to be lower than the value (232.94±11.45 to 2223.68±33.48 mg catechol/100 g) reported for few indigenous rice including pigmented rice germplasms of Assam (
Mudoi and Das, 2019).
The total phenol content of different products and their intermittent forms varied from 65.16 mg/100 g-80.29 mg catechol equivalent /100 g, the lowest was observed in
komal chaul and the highest in intermittent form 2.
The phenolic compounds are localized mainly in the external layers of the grain
(Walter and Marchesan, 2011); the bran contains between 70 and 90% of the phenolic acids in light brown pericarp of rice grains
(Zhou et al., 2004). The bran contains approximately 85% of the anthocyanins in the rice grains with black pericarp, with little variation depending on the cultivar and the compounds considered
(Hu et al., 2003). As phenolic compounds are water soluble, soaking might be the reason for the observed decrease in the total phenol content in
hurum, komal chaul, flaked rice and the two intermediate forms. However, the decrease observed in
korai and the slight increase for
sandah guri might be due to change in percentage as the hard portions were eliminated by sieving.
The total ash content of brown form was found to be 0.66% to 0.92%. Similar observations on ash content were reported for some brown form of
chakua rice varieties (0.66% -1.52%)
(Das et al., 2018) and for some indigenous red cultivars of brown rice of Assam (0.73%-1.85) (Mudoi and Das, 2018) respectively.
The ash content of different products and their intermittent forms varied from 0.75%-1.34%, the lowest was observed in intermittent product 1 and the highest in
hurum. Similar observations were reported for some traditional rice products of Assam
(Banik et al., 2018). Soaking changed fibre, ash and mineral compositions in rice and also brought diffusion of color pigments, fat globules, etc, from husk and bran layers into starchy endosperm
(Kale et al., 2015).
The observed higher ash content in
korai than the respective raw form might be mainly due to increase in percentage as during sieving, a hard portion which was greater in size (more than 50 μ) was rejected. The hard portion might be composed of starch as during this step, significant decrease in starch content was also observed
(Bhattacharjee et al., 2019). As
sandah guri was also collected after sieving, the increase in ash content can be justified as mentioned above.
The phosphorus content of brown form of specialty rice were found to be 337.33 to 494.50 mg/100 g
. The phosphorus content of some brown form of
chakua rice varieties of Assam ranged from 173.95 mg/100 g (
Lahi chakua) to 328.78 mg/100 g (
Pozo chakua)
(Das et al., 2018).
The phosphorus content of different products and their intermittent forms was found to be 250.26 to 383.20 mg/100 g, the lowest was observed in
bhoja bora and the highest in intermittent product 2.
The decrease in phosphorus content in
komal chaul and flaked rice and in both the intermittent forms might be attributed to soaking leading to loss of this mineral in the form of phytic acid. However, both the decrease of phosphorus in
korai than
Michi bora, in
sandahguri than
komal chaul, in
bhoja bora than intermittent form 1 and in
hurum than the respective intermittent form 2 might be attributed to change in percentage only due to associated increase in other dry matter components.
The iron content of brown form was found to be 2.13 to 3.39 mg/100 g, which was found to be lower than the values (2.12-54.40 mg/100 gm) reported for pigmented rice varieties of Assam (
Mudoi and Das, 2019).
The iron content of different products and their intermittent forms varied from 2.47-6.91 mg/100 g, the lowest was observed in
komal chaul and the highest in
korai.
It was reported that the higher iron content detected after soaking might be due to absorption of water containing iron (
Kumar and Prasad, 2018). However, the present observation of gradual increase in iron content in both intermittent forms and final products might be due to decrease in percentage of other minerals (P, Ca, Na and K), not actual increase.
The zinc content of brown form was found to be 2.14 to 2.51 mg/100 g. The zinc content of present investigation was found to be lower than the values (2.42- 26.57 mg/100 g) reported for some indigenous red rice germplasm of Assam (
Mudoi and Das, 2019 and
Mudoi and Das, 2022).
The zinc content of different products and their intermittent forms was found to be 2.93 to 4.08 mg/100 g, the lowest was observed in intermittent form 2 and the highest in
hurum.
The present observation of gradual increase in zinc content in both intermittent forms and final products might be due to decrease in percentage of other minerals (P, Ca, Na and K), not actual increase.
The calcium content of brown form was found to be 21.67-27.67 mg/100 g. The calcium content of different products and their intermittent forms was found to be 11.32 -23.34 mg/100 g. The calcium content of roasted rice and flaked rice were 18.43 mg/100 g±0.20 and 18.40±0.26 mg/100 g, respectively (
Kumar and Prasad, 2018).
The observed gradual decrease of calcium in all the products except in processing of
sandahguri from
kumal chaul and
korai from
michi bora might be attributed to loss of calcium during soaking. The processing of paddy involved soaking and heating, during which the minerals were either leached out or removed from the grain (
Kumar and Prasad, 2018). However, the decrease in calcium content in
korai than michi bora might be attributed to discarding calcium containing components during sieving and increase in
sandahguri than
kumal chaul might be associated with decrease in percentage of other components only, not actual change.
The sodium content of brown form was found to be 58.67 (
Michi bora) to 63.31 mg/100 g (
Ronga chakua). It was reported that the sodium content of some brown form of
chakua rice varieties of Assam ranged from 14.82 mg/100 g -22.70 mg/100 g
(Das et al., 2018). The sodium content of different products and their intermittent forms was found to be 37.33 (
bhoja bora) to 56.67 mg/100 g (
sandah guri)
.
The potassium content of brown form of specialty rice was found to be 216.33 (
Michi bora) to 220.33 mg/100 g (
Bakul bora)
. Das et al., 2018 reported that the potassium content of some brown form of
chakua rice varieties of Assam ranged from 84.71 mg/100 g-287.6 mg/100 g.
The potassium content of different products and their intermittent forms was found to be 64.32 (
bhoja bora) to 212.31 mg/100 g (intermittent form 2).
Kumar and Prasad, 2018 reported that the potassium content of roasted rice and flaked rice were 119.0±1.73 mg/100 g and 154.0±6.24 mg/100 g, respectively and the processing of paddy involving soaking and heating, might cause the minerals either leached out or removed from the grain.
