Enzymatic Process for Pigeon Pea

Abstract

Pigeon pea is generally used as a dhal i.e., in split form therefore, it is important to check its splitting i.e., hulling efficiency and maximum dhal recovery. Pre-treatments are commonly given for loosening and removing of the seed coat with retaining its edible portion. Enzymes viz. xylanase, pectinase and cellulose were applied to evaluate the dehusking properties of pigeon pea grains. The effect of four enzymatic parameters, i.e., enzyme concentration (20–50 mg 100 g−1 dry matter), incubation time (4–12 h), incubation temperature (35–55°C) and tempering water pH (4.0–6.0) on dehusking efficiency were optimized with statistical package response surface methodology (RSM). In which the hulling efficiency with a high value for the coefficient of determination R2 (0.92) described satisfactorily quadratic model. It predicted 76.54–82.80% hulling efficiency, 20.70–25.30% protein content and 12.42–15.10 min cooking time at optimized enzyme concentration of 27.64–31.34%, incubation time 7–9 h, incubation temperature 43–45°C and 5–6 pH value for different varieties of pigeon pea as compared to 66.00–78.30% hulling efficiency, 18.74–21.81% protein content and 13.23–18.00 min cooking time for traditional oil treatment. It shown that increased hulling efficiency and protein content and decreased cooking time for enzyme pretreated pigeon pea compared to the oil pretreated method.

1. Introduction

Pulses are mostly consumed as a dhal, it is important to dehusk and then split into two parts. Pigeon pea is very hard to dehusk hence pre-treatment is essential before milling practice. Pre milling treatments are commonly carried out to loosen the seed coat to eliminate husk without dropping any fit for human consumption element and higher dhal recovery. Pigeon pea is commonly processed to mend their cooking and nutritional traits. Dehusking of pigeon pea also aids to get rid of antinutritional compounds which include polyphenols observed in the seed coat. Pretreatment for loosening of the seed coat from the grain is one of the essential stages in dehulling of pigeon pea. This process is usually completed by way of the use of mechanical means. Grain pretreatment is commonly intended to harden the hull and slacken the gummy bond between the hull and the cotyledon and to strengthen the cotyledon to lessen damage. Removal of the seed coat at some stage in dehusking is conventionally completed either through moist or dry methods [1]. Pretreatments may additionally include thermal treatment only or soaking in water, chemical solutions, etc. [2, 3, 4, 5]. These treatments results shape deformation of split or poor cooking quality of splits. These treatments needs more labour and consume more time.

Several preceding research pronounced that the husk of grain adhered to the cotyledons due to the presence of calactomonus disaccharide, glucoronai acid and glycol protein [6]. Swamy et al. [7] reported that for adherence of husk to the cotyledons, arabinogalactan type polysaccharide is responsible, which possess the gummy and hygroscopic nature. Those complicated biological compound makes the removal of seed coat of pigeon pea a tough technique. Hence, making of dhal without pretreatment consequences in low dhal availability. Saxena [8] suggested that pre-treatments has an essential function in increasing dhal recuperation by means of slackening seed coat from cotyledons. Consequently Phirke and Bhole [3] advised specific pre-treatments viz., water soaking, water spray with oil treatment, sodium bicarbonate treatment and enzyme treatment except sodium bicarbonate treatment induced widespread loss in protein content of cotyledons over untreated samples. Saxena [8] said that the outcomes of seed coat elimination by chemical treatment of pigeon pea grain through the usage of calcium hydroxide, sodium hydroxide and sodium bicarbonate aqueous solutions was observed and among them sodium bicarbonate solution turned into the very much result of dhal availability. Sharanagouda et al. [9] suggested the use of mustard oil treatment for Gulyal variety to get higher unhulled grains during milling (79.4%) and dhal (68.8%) in comparison of Maruti and Asha variety. Whereas Maruti (76.5%) and Asha (56.9%) variety resulted higher unhulled grains by acetic acid treatment. ‘Sirka’ may be utilized instead of oil for pigeon pea milling [10]. Dhal availability in this procedure became extra or less identical as in case of oil treatment.

It was reported that pigeon pea is tough-to remove seed coat because of the existence of mucilage and gum bring into being a sturdy bond among the seed coat and cotyledons. The mucilage and gums exist in between the husk and cotyledons show an essential function within the removal process of seed coat of pigeon pea due to its chemical nature [4]. Cosgrove [11] observed that mucilages and gums of pigeon pea grains are complex of cellulosic micro fibrils fixed in a medium of non-starch polysaccharides (NSP) and proteins. Through the enzymatic reactions, fractional hydrolysis of those NSP and/or proteins also enable the easy removal of seed coat of pulses [12, 13]. Sreerama et al. [14] mentioned enzyme treatment better than thermal treatment as xylanase intervened degradation of cell wall polysaccharides of horse gram bring about in enlargement of the grain with stepped forward nutritional and functional properties. Sreerama et al. [15] reported protease or sodium bicarbonate pre-treatments develop the physical and enlargement properties of pigeon pea and horse gram.

Reddy et al. [16] studied the protein deposition pattern in pigeon pea seed and reported that the outer layers of the cotyledons are richer in protein in evaluation to inner layers of seed. From vitamins point of view, that is a considerable that dehulling no longer reduces protein-rich germ but additionally the outer layers of the cotyledons wherein distinctly extra protein components are covered. Fortuitously, the protein high-quality in phrases of amino acids is not adversely laid low with removal of seed coat. Singh and Jambunathan [17] similarly pronounced that removal of seed coat process also reduces about 20% calcium and 30% iron. To maintain the beneficial value of pigeon pea seed and minimizing the nutrient losses for the process of dehulling it is essential that extra effective dehulling process is developed and transferred to rural areas wherein through and large milling continues to be executed with the aid of inefficient old-age strategies. In line with Kurien [1] in control situations the dhal recovery obtains the most efficiently up to 80–84% however at industrial the recovery stays round 70%. It was mentioned the reason of different variety (72–82%) for dhal yield. Consequently, it could be expected that for a mixture of a different variety and a competent pigeon pea process, there is possibility to reduce the nutrient losses.

Enzyme pre-treatment resulted 13.81% higher recovery of dhal compared to oil treatment for pigeon pea [18]. Murumkar et al. [19] reported the dhal recovery (76.60%) and milling efficiency (96.19%) with optimized enzymatic hydrolysis parameters. Enzymes makes the possibility of the fractional disruption/degradation of non-starch polysaccharides and/or proteins of mucilage that is found at interface between hulls and cotyledon. Green gram and black gram pretreated with protease resulted better yield of dehulled grain. In case of horse gram xylanase pre-treatment was very powerful in improving the dehulling process as compared to protease. Whereas for red grain, protease pre-treatment produced greater dehulled than xylanase. It is also evident that the enzyme dehulling pre-treatments no longer only expanded the dehulling performance, however additionally decreased the quantity of powder and fines [20]. Enzyme dispensed with object grains have been observed to make reduction of dehusking time as compared to water treated grains utilized in traditional milling. The enzyme treated grains were resulted to be brighter in contrast to untreated grains. Additionally, there have been adjustments found in the quantity of damaged grains and powder formation i.e., after processing of the grains, the powder formation and wide variety of broken grains decreased extensively which bolsters the overall purpose for application of enzymes for dehusking [21].

Pre milling treatments are commonly employed to loosen the seed coat to dispose of husk without losing any suitable for eating portion. There are many milling strategies like wet milling, dry milling, Central Food Technological Research Institute (CFTRI) technique, Pantnagar method, Central Institute of Agricultural Engineering (CIAE) method and Indian Institute of Pulse Research (IIPR) method advanced for pigeon pea milling. The above stated techniques are time ingesting, require almost four to seven days for the entire milling of pigeon pea. Also, the survey work of few pulse mills in Gujarat revealed that the dry milling treatments achieved at some stage in the milling for pigeon pea take longer processing time, approximately seven to eight days depending upon climate as sun drying is needed to get agreeable milling after pre-treatment [22]. But, these kinds of techniques do not allow easy elimination of seed coat in the course of the following processing operation of pigeon pea milling. Furthermore, those pre-treatments cause enhanced processing charge, longer processing time and labour consuming for pigeon pea milling. It was revealed that the exquisite potentiality of technology up gradation exists to get higher recovery of dhal in addition to lessening in processing time and energy required [22].

This necessitated the proper pre-treatment for pigeon pea milling which could shorten the processing time and improve the product value. The charge for the milled product is fixed on the idea of number of grains with intact husk (in part or entirely) in the pattern, chipping of edges of the cotyledons, volume of floor scouring of the grain, and the variety of the pigeon pea. Dhal with a lesser or no husk, natural luster, yellow in coloration and sharp edges of break up cotyledons, can be sold in the market at a better price.

It is far important to have unique pre-treatment to dissolve the glue that binds the cotyledons of pigeon pea grains to the seed coat. It is almost obvious that de-hulling quality is particularly depending on physical quality of grains and pre-treatments. Selection of pre milling treatment also relies upon on the characteristics of the grain. In addition, pre-treatments given to pigeon pea grains earlier than de-hulling considerably influence the cooking time. The cooking quality of pigeon pea is essentially assessed with the aid of its cooking time [23].

The mechanism of enzymatic activity is governed by using four interacting parameters, i.e., grain moisture content material, enzyme concentration, reaction time and incubation temperature [24]. Foremost ranges of those parameters are necessary to get most recovery and higher quality of dhal. Facts on the effect of above parameters on de-hulled fractions and cooking high-quality seems to be missing. Several reviews are to be had for food grade activities of enzymes i.e., xylanase and cellulase as husk loosening agent in many grains. By way of this reaction of enzymatic treatments lesser force will be required to result in the de-husking and thereby lower in processing time and cost.

Chemical composition and binding material at the interface of seed coat and cotyledon decides the choice of enzymes. Saxena and Srivastava [25] suggested that bio-bleaching agent for lignin isolation is the xylanase. Cellulose to beta-glucose and pectin to pectic acid converted by cellulase and pectinase, respectively. Consequently, xylanase, cellulase, and pectinase are the important enzymes that ruin down the binding factors that lead to multiplied efficacy.

2. Material and methods

Preliminary trials are essential to achieve standard proportions of enzymes, i.e., xylanase: pectinase: cellulase to get the most out of the husk removal. The outcome of selected enzyme combination on husk removal of pigeon pea grain is to be assessed keeping the enzyme concentration, incubation time, incubation temperature and tempering water pH constant based on the technical specifications of the products delivered by manufacturer.

Following equations are to be used to calculate husk removal and hulling efficiency [26].

$$\mathit{Husk}\mathit{removed}\left(HR\right)\%=\frac{\mathit{Husk}\mathit{Removed}\mathit{during}\mathit{dehusking}}{\mathit{Total}\mathit{husk}\mathit{content}}\times 100$$E1

$$\mathit{Coefficient}\mathit{of}\mathit{hulling}\left(Ch\right)=1-\frac{\mathit{Weight}\mathit{of}\mathit{unhulled}\mathit{grain}\mathit{after}\mathit{milling}}{\mathit{Weight}\mathit{of}\mathit{unhulled}\mathit{grain}\mathit{used}for\mathit{milling}}$$E2

$$\mathit{Coefficient}\mathit{of}\mathit{wholeness}\mathit{of}\mathit{kernel}\left(Cwk\right)=\frac{W_f}{W_f+W_b+W_p}$$E3

where W_f = weight of finished product; W_b = weight of brokens; W_p = weight of powder.

$$\mathit{Hulling}\mathit{efficiency}=Ch\times Cwk\times 100$$E4

3. Enzymatic pre-treatment

The enzyme solutions are to be made with the standardized percentage of all three decided enzymes. On this enzymatic pre-treatment method, the degumming is probably because of the reaction of different enzymes used for pre-treatment, i.e., xylanase, pectinase and cellulase. Because the enzyme activities relies upon on temperature, pH and incubation duration, crucial parameters at the side of the enzyme proportions, temperature, pH and incubation duration is to be taken into consideration.

4. Dehulled sample separation

The dissimilar fractions of the milled product which include whole dehulled grains, divided dehulled grains, in part dehulled and unhulled grains, broken, husk and powder are to be separated using suitable sieves (BS sieves no. 4, 6, 18). A grain is to be taken into consideration completely dehulled whilst there has been no husk adhering to it.

5. Cooking time

Pigeon pea dhal are to be cooked in a stainless steel pan having a ratio of dhal: distilled water as 1:10. For observation of cooking time, throughout boiling, the level of water is to be maintained by means of regular addition of boiled water. Boiling is to be persisted and grains to be drawn at 1 min interval to test the cooking time by way of pressing between the thumb and the forefinger till no hard core is left as described by way of [23]. Full cooking time is to be documented as the time while ninety percent of the dhal became gentle sufficient to masticate [27].

In an experiment the observation of different enzyme pretreatment were recorded. The best combination of enzyme concentration, incubation temperature, incubation time and pH were selected with respect to hulling efficiency, cooking time and protein content.

The statistical analysis was carried out of experimental data and the significant effect of enzyme concentration, incubation temperature, incubation period and tempering water pH along with their interactions on hulling efficiency, cooking time and protein content were calculated.

6. Results and discussion

6.1 Effect of enzyme pretreatment parameters on hulling efficiency

The enzymatic pre-treatment for pigeon pea process resulted hulling efficiency in the range of 76.90–82.80% which was higher than dry milling method which was in the range of 66–78.30%. This is due the effects of incubation temperature on hulling efficiency (p < 0.001). This finding was confirmed by [18, 19]. Hulling efficiency was also significantly affected by tempering water pH. Sangani et al. [18] additionally mentioned effect of pH on hulling efficiency. Hulling efficiency was significantly affected by enzyme concentration [19, 20, 21] but [18] observed the non-significant effect of enzyme concentration on hulling efficiency. Outcomes of incubation time have been determined large effect on hulling efficiency (p < 0.01) [18, 19]. Opoku et al. [28] marked tempering is vital for reaching better dehulling results after soaking and drying or steaming and drying.

6.2 Effect of enzyme pretreatment parameters on protein content

The enzymatic treatment for pigeon pea process resulted protein content in the range of 20.70–25.30% which was higher than dry milling method which was in the range of 18.74–21.81%. Singh and Jambunathan [17] reported that dehulling process resulted scarification of outer layers of cotyledons and hence 12% yield loss as powder fraction. The outer surface of cotyledons is an affluent supply of protein, sugar, fiber, and ash but scanty in starch. Protein content of dhal by enzymatic pre-treatment was affected by enzyme concentration, incubation period and pH. However, outcomes of incubation temperature had significant effect on protein content (p < 0.01). Chandini et al. [21] also reported that crude protein in pigeon pea was affected by higher soaking time. This may because crude protein possess hydrophilic property which could have leached out while soaking in water. Murumkar et al. [19] reported enzyme pre-treatment to pigeon pea increased 2.96% protein content. Tiwari et al. [29] also reported increases of the protein content due to pre-treatment. The pectinase having high polygalacturonase activity was the most effective preparation in terms of protein release. Rommi et al. [30] reported enzymatic carbohydrate hydrolysis correlated with increased protein extractability at tempering water pH 6. Das et al. [31] reported increase in proteins by cellulase pre-treatment in milled rice.

6.3 Effect of enzyme pretreatment parameters on cooking time

The enzymatic treatment for pigeon pea process resulted cooking time in the range of 12.42–15.10% which was lower than dry milling method which was in the range of 13.23–18.00%. It was reported that effects of enzyme concentration, incubation time and tempering water pH had significant effect on cooking time (p < 0.001). However, results of incubation temperature changed into non-significant impact on cooking time. Sangani et al. [32] showed the significant effect (p < 0.05) of enzyme concentration and tempering water pH, and they observed highly significant effect (p < 0.01) of incubation time. He also determined non-significant effect of all the interplay on cooking time. Bhokre and Joshi [33] also pronounced that the cooking time reduces by soaking of cowpea. Tiwari et al. [29] also mentioned the effect of conditioning on cooking time. The effect of enzyme pre-treatment on cooking time was reported for pigeon pea, chick pea and other legumes. [19, 34]. Inversely Sreerama et al. [20] was observed no noteworthy change inside the cooking times of dehulled splits for control and enzyme (xylanase and protease) pre-treated with legumes.

Thus it could be concluded that the enzymatic pre-treatment for pigeon pea process resulted higher hulling efficiency, higher protein content and lower cooking time as compared to dry milling method of pigeon pea processing. This method not only giving better recovery and quality, but it reduces the time for processing from 5 days to 1 day.

7. Conclusions

Important parameters for pigeon pea processing are hulling efficiency, protein content and cooking time requirement. It was found that traditional method of oil treatment for pigeon pea processing resulted in the range of 66.00–78.30% hulling efficiency, 18.74–21.81% protein content and 13.23–18.00 min cooking time; whereas enzymatic pretreated pigeon pea processing resulted 76.54–82.80% hulling efficiency, 20.70–25.30% protein content and 12.42–15.10 min cooking time at optimized enzyme concentration of 27.64–31.34%, incubation time 7–9 h, incubation temperature 43–45°C and 5–6 pH value. This process not only increased the hulling efficiency but it reduces the time requirement of process.

Conflict of interest

I declare that it will not be published elsewhere in the same form, in English or in any other language, including electronically without the written consent of the copyright holder.