Organic dry pea (Pisum sativum L.): A sustainable alternative pulse-based protein for human health

Dry pea (Pisum sativum L.) is a cool-season food legume rich in protein (20–25%). With increasing health and ecosystem awareness, organic plant-based protein demand has increased; however, the protein quality of organic dry pea has not been well studied. This study determined the genetic variation of individual amino acids (AAs), total AAs (liberated), total protein, and in vitro protein digestibility of commercial dry pea cultivars grown in organic on-farm fields to inform the development of protein-biofortified cultivars. Twenty-five dry pea cultivars were grown in two USDA-certified organic on-farm locations in South Carolina (SC), USA, for two years (two locations in 2019 and one in 2020). The concentrations of most individual AAs (15 of 17) and the total AA concentration significantly varied with dry pea cultivar. In vitro protein digestibility was not affected by the cultivar. Seed total AA and protein for dry pea ranged from 11.8 to 22.2 and 12.6 to 27.6 g/100 g, respectively, with heritability estimates of 0.19 to 0.25. In vitro protein digestibility and protein digestibility corrected AA score (PDCAAS) ranged from 83 to 95% and 0.18 to 0.64, respectively. Heritability estimates for individual AAs ranged from 0.08 to 0.42; principal component (PCA) analysis showed five significant AA clusters. Cultivar Fiddle had significantly higher total AA (19.6 g/100 g) and digestibility (88.5%) than all other cultivars. CDC Amarillo and Jetset were significantly higher in cystine (Cys), and CDC Inca and CDC Striker were significantly higher in methionine (Met) than other cultivars; CDC Spectrum was the best option in terms of high levels of both Cys and Met. Lysine (Lys) concentration did not vary with cultivar. A 100 g serving of organic dry pea provides a significant portion of the recommended daily allowance of six essential AAs (14–189%) and daily protein (22–48%) for an average adult weighing 72 kg. Overall, this study shows organic dry pea has excellent protein quality, significant amounts of sulfur-containing AAs and Lys, and good protein digestibility, and thus has good potential for future plant-based food production. Further genetic studies are warranted with genetically diverse panels to identify candidate genes and target parents to develop nutritionally superior cultivars for organic protein production.

significantly varied with dry pea cultivar. In vitro protein digestibility was not affected by cultivar.

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Total AA and protein for dry pea seeds ranged from 11.8 to 22.2 and 12.6 to 27.6 g/100 g, 36 respectively, with heritability estimates of 0.19 to 0.25. In vitro protein digestibility and protein 37 digestibility corrected AA score (PDCAAS) ranged from 83 to 95% and 18 to 64, respectively. to identify suitable cultivars for organic production with increased nutrition quality. were hand cleaned, finely ground using a UDY grinder, and stored at −10 °C until protein quality 137 analysis. All protein quality data are reported on a dry mass basis (15% moisture).  Estimates were based on a 72 kg adult consuming 100 g of dry pea (15% moisture content) per Lys (Table 2).

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Protein quality: Organic dry pea cultivars had values of 11.8 to 22.2 g/100 g for total AAs 215 (liberated), 12.6 to 27.6 g/100 g for total protein, 18 to 64 for PDCAAS value, and 83 to 95% for 216 in vitro protein digestibility (Table 3). Dry pea contained a range of individual AAs, including 217 nine essential AAs with a mean of 0.22 g/100 g for SAAs and 0.88 g/100 g for Lys (Table 3). 218 These organic dry pea cultivars provide a significant amount of the recommended daily allowance AAs, and in vitro protein digestibility (Fig. 2). Out of 175 observations, 6.4% were high in Cys 233 and Met, 8.8% were high in total AAs, and 5.6% were high for in vitro protein digestibility (Fig.   234   2). Among the 25 cultivars tested, 10 cultivars showed more than 18 g/100 g of total AAs, with 235 Fiddle being the highest and AAC Carver and AC Earlystar the lowest (Fig. 3). For in vitro protein 236 digestibility, 17 of 25 cultivars showed a digestibility of 87% or better, with Fiddle having the 237 highest value and AAC Carver the lowest (Fig. 3). CDC Saffron, CDC Spectrum, and CDC Striker 238 showed significantly higher concentrations of SAAs than AAC Carver and AC Earlystar (Fig. 4).

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AAC Comfort showed higher Lys concentrations than other cultivars, but the effects were not 240 significant (Fig. 4). Our results demonstrate that current dry pea cultivars bred for conventional systems vary in terms 244 of seed AA profile, total AAs, total protein, and in vitro protein digestibility when grown under 245 organic cropping systems. Organic dry pea is a rich source of essential AAs, as a 100 g serving of 246 organic dry pea provides 0.02-3.07 g/100 g of nine essential AAs (14-180% of RDA), 11.8-22.2 g 247 of total AAs, and 22-48% of the daily protein requirement, with an in vitro protein digestibility of 248 83-95% (Table 3). In contrast to previous literature that states pulses are generally low in SAAs,

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our results demonstrate organic dry pea is a good source of SAAs (Met and Cys), with a 100 g 250 serving providing 220 mg of total SAAs (Met+Cys) and 1.33 g of Lys (Table 3; Fig. 4) [30,31].

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According to our knowledge, this study is the first report on the detailed protein quality of 252 commercial dry pea cultivars grown in an organic system towards protein biofortification.

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The organic dry pea cultivars in this study had mean protein and total AA (liberated) 254 concentrations of 20.9 g/100 g and 17.5 g/100 g, respectively (Table 3). Several dry pea cultivars 255 had high total AAs (>18 g/100 g) and >87% in vitro protein digestibility (Fig. 3), demonstrating 256 they are suitable for organic plant-based protein production. Among the cultivars tested, Fiddle 257 had the highest total AA concentrations (19.6 g/100 g), and AAC Carver (15.5 g/100 g) and AC 258 Earlystar (16.1 g/100 g) the lowest. Our previous study on the agronomic adaptability of dry pea

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[4] indicated AAC Carver, Jetset, and Mystique as the highest yielding cultivars (>2000 kg/ha) 260 and most suitable for organic production without a yield penalty compared to conventional 261 growing systems. However, the current study indicates these three cultivars have low total AAs 262 and in vitro protein digestibility (Fig. 3) protein digestibility (Fig. 3) of organic dry pea in component 1, and one essential AA (His) in component 2 (Fig. 1). These 289 essential AAs are also positively correlated with total AA, protein, and in vitro digestibility ( AAs. These proteins have several limitations in terms of human nutrition: they often lack one or 310 more essential AAs, they are often not fully digestible, and toxins and pesticides are concentrated 311 during protein extraction and drying procedures. Therefore, pursuing nutritional breeding or 312 biofortification of dry pea using an organic system approach is vital to overcome these nutritional 313 and production issues for pulse growers and consumers. Organic nutritional breeding of pulses is 314 challenging and demands better phenotyping and genetic resources for cultivar development. With 315 the increasing availability of genomic resources, expanding organic pulse breeding targets to 316 produce better quality proteins with higher digestibility will be possible in the future.      as well as for total AA concentration. Estimates were for a 72 kg adult consuming 100 g of dry pea (15% moisture content) per day 481 given the following dietary requirements: 8-12 mg/kg His, 10 mg/kg Iso, 14 mg/kg Leu, 12 mg/kg Lys, 13 mg/kg Met + Cys, 14 mg/kg 482 Phe + Tyr, 10 mg/kg Val, and 0.8 g/kg protein [29].