Nutritional characterization of peas and effect of microwave deactivation

Internationally, corn and soybeans showed a price increase of 88% and 57% in the last 24 months, respectively (IndexMundi, 2022).

This price increase motivates the need to look for alternative ingredients in order to reduce costs.

The pea, pea or pea (Pisum sativum) is presented as a viable alternative in our country. Argentina’s INASE (National Seed Institute, 2022) has more than 87 registered varieties that can be green or yellow.

Being the most planted cultivars are the Viper for green peas and the Yams for yellow peas (Prieto, 2009).

The pea grain is an ingredient with good potential for animal feed, it is characterized by having:

High crude protein content (20-26%)

Good palatability

Low content of antinutritional factors  (Galméus, 2012;  de Blas et al. , 2019).

Its protein, consisting of albumins and globulins, is deficient in sulfur amino acids and tryptophan, but rich in lysine.

The digestibility of protein and amino acids is similar to that of soybean meal. It has low fat and a high starch content (42-51%) (de Blas et al., 2019).

Generally speaking, legumes are characterized by the presence of anti-nutritional factors, such as:

 Trypsin inhibitors

Phyto-hemaglutinins

Cyanogenic glycosides

Saponins

 Alkaloids

Non Protein Amino Acids (Cubero & Moreno, 1983; Monari, 1996),which negatively affect the productive performance of birds (Iglesias & Azcona, 2012).

Objectives

• Nutritionally characterize two pea cultivars, one green and one yellow.
• To assess the effect of microwave deactivation.

Materials and methods

Pea samples were taken from the Viper and Yams cultivars, green and yellow respectively, from the 2019 and 2020 campaigns grown in Argentina. On which it was determined:

• Dry Matter
• Crude Protein (CP) mediante el método Kjeldahl
• Ether Extract (EE) extraído con hexano
• Crude Fiber (CF)
• Ashes
• Starch

Neutral detergent fiber (NDF) was also determined through the Goering and Van Soest method (1970), with the addition of α-amylase. Acid detergent fiber (ADF) was determined according to Van Soest methodology(1963).

In addition, urease activity and trypsin inhibitors were measured.

To complement the chemical characterization, true metabolizable energy (ME) was determined (Sibbald, 1976), as well as its nitrogen correction(MEn), using 6 roosters per sample.

A 200 g sample of raw peas in the form of a monolayer was placed on a microwave dish  with a 900 Watts power output. It was cooked at 70% power for different cooking times (0, 3, 5,  6, 7 and 9 min), in 3 batches (repetitions) (Chale et al.,  2017) This process was carried out to evaluate the effects of microwave deactivation.

A completely randomized design with 6 treatments and 3 repetitions each was used.

The analyses that were performed on the sample were:

Dry matter

Crude protein using the Kjeldahl method

 Urease activity (UA)

Protein solubility (PS)

Insoluble nitrogen in acid detergent (INAD)

True metabolizable energy through the Sibbald method(1976). 3 roosters were used per repetition.

The data was submitted to analysis of variance (ANOVA). When the degree of significance was less than 5%, the means comparison was performed through the minimum significant differences test(Di Rienzo et al. , 2020).

Results and discussion

Nutritional composition

Table 1 shows the composition results of Viper and Yams peas from the 2019 and 2020 campaigns, as well as the pea values published on FEDNA tables (de Blas et al. , 2019).

Table 1. Treatments.Table 1.  Data standardized to 88% DM, except dry matter. GE: Gross energy; TME, True metabolizable energy; TMEn: True metabolizable energy corrected by nitrogen. *Source: (de Blas et al., 2019).

Although a statistical analysis has not been carried out due to the few samples analyzed, no major differences have been found between cultivars and between campaigns.

The parameters that were most affected by the cultivar, and also by the campaign, were those related to fiber, either CF, NDF and ADF.  And only between campaigns were important differences observed in EE, but this did not affect CE values.

Effect of microwave deactivation

Table 2 shows the results of pea deactivation through the use of microwaves.

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Table 2.  Effect of microwave pea deactivation on chemical parameters.*Data standardized to 88% DM. MS: Dry matter; PB, Crude protein; AU, Urease activity; PS, KOH soluble protein 0.2%; NIDA: Insoluble nitrogen in acid detergent. Means with different superscript differ statistically (p≤0.05).

As the cooking time increased, and as expected, the humidity of the sample decreased, so the percentage of DM increased linearly (p≤0.05). Whereas, the percentage of protein standardized to 88% DM was not affected by cooking time (p>0.05).

With urease activity, a linear effect was found due to cooking time (p≤0.05), as in PS in KOH.

In the case of NIDA, the response was quadratic (p≤0.05), but this parameter was less sensitive, since a significant difference was only found after 9 min of cooking (p≤0.05).

In Table 3 you can find the energy values according to the different cooking times.

Energy Parameters

Table 3.Effects of microwave deactivation of peas on energy parameters.Table 3.  Effect of deactivating peas with microwaves on energy parameters. Data standardized to 88% of DM. EMV: True metabolizable energy; EB: Gross energy. 9 Means with different superscripts, differ statistically (p≤0.05).

Regarding the energy analysis, as the cooking time increased, the EMV of the sample increased significantly (p≤0.05), reaching a maximum of 5 min of cooking (+204 kcal / kg with respect to crude oil), as well as what happens with the use of EB (EMV / EB), clearly observing a quadratic response in these parameters (p≤0, 05, Table 3 and Figure 1).

A similar situation was observed with soybeans, but the time needed to achieve optimal microwave deactivation was 6 min (Chale et al., 2017).

Figure 1.  Effect of microwave pea deactivation on true ME and gross energy utilization.

Conclusions

Nutritional characterization of peas

No major differences were found between pea cultivars, nor between crop campaigns (2019 and 2020). The parameters that varied the most were CF, NDF and ADF.

Effects of microwave deactivation

Although peas have low levels of antinutritional factors, a beneficial effect was found when applying a thermal process using microwaves. It was established that with 5 min of cooking at 70% power in a microwave of 900 watts the best results of EMV and use of the EB are achieved.