Nitrogen-to-Protein Conversion Factors for Crop Residues and Animal

Oct 2, 2017 - Biomass and Bioresource Utilization Laboratory, College of Engineering, China Agricultural University, Beijing 100083, P.R. China .... p...
0 downloads 8 Views 573KB Size
Subscriber access provided by LONDON METROPOLITAN UNIV

Article

Nitrogen-to-Protein Conversion Factors for Crop Residues and Animal Manure Common in China Xueli Chen, Guanglu Zhao, Yang Zhang, Lujia Han, and Weihua XIAO J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.7b03441 • Publication Date (Web): 02 Oct 2017 Downloaded from http://pubs.acs.org on October 3, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Journal of Agricultural and Food Chemistry is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 25

Journal of Agricultural and Food Chemistry

1

Nitrogen-to-Protein Conversion Factors for Crop Residues and Animal Manure

2

Common in China

3 4

Xueli Chen, Guanglu Zhao, Yang Zhang, Lujia Han, and Weihua Xiao*

5 6

Biomass and Bioresource Utilization Laboratory, College of Engineering, China

7

Agricultural University, P.R. China 100083

8 9 10

Corresponding Author * E-mail: [email protected]; Phone: +86 10 6273 6778; Fax: +86-10-6273-6778

1

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

11

ABSTRACT: Accurately determining protein content is essential in exploiting

12

biomass as feed and fuel. A survey of biomass samples in China indicated protein

13

contents from 2.65 to 3.98 % for crop residues and from 6.07 to 10.24 % for animal

14

manure of dry basis. Conversion factors based on amino acid nitrogen (kA) ranged from

15

5.42 to 6.00 for the former and from 4.78 to 5.36 for the latter, indicating that the

16

traditional factor of 6.25 is not suitable for biomass samples. On the other hand,

17

conversion factors from Kjeldahl nitrogen (kP) ranged from 3.97 to 4.57 and from 2.76

18

to 4.31 for crop residues and animal manure, respectively. Of note, conversion factors

19

were strongly affected by amino acid composition and levels of nonprotein nitrogen.

20

Thus, kP values of 4.23 for crop residues, 4.11 for livestock manure, and 3.11 for

21

poultry manure are recommended to better estimate protein content from total nitrogen.

22 23

KEYWORDS: crop residues, animal manure, amide acid, protein, nitrogen-to-protein

24

conversion factor

2

ACS Paragon Plus Environment

Page 2 of 25

Page 3 of 25

Journal of Agricultural and Food Chemistry

25

1. INTRODUCTION

26

Crop residues and animal manure, which are widely and abundantly available,1,2

27

have both actual and potential value as source of proteins. For example, crop residues

28

are frequently used as animal feed and nitrogen source for anaerobic fermentation

29

because of their high protein content.3 Animal manure, similarly rich in protein, is also

30

well known as a significant source of bioenergy, as fertilizer, or as animal feed.4-6

31

Indeed, many forms of biomass are potentially useful as such, but have unknown

32

protein content. Therefore, it is essential to develop a rapid and reasonably accurate

33

method to determine protein content. Presently, there are four main analytical methods

34

for food labeling purpose,7 including copper- or dye-based spectroscopy, UV- or

35

IR-based techniques, amino acid analysis, and conversion of nitrogen content to protein

36

content.

37

Total nitrogen analysis by the Kjeldahl method is still widely favored as a basis of

38

protein content determination, but its accuracy depends on nitrogen-to-protein

39

conversion factors. In previous articles, Fujihara and colleagues8-10 reported

40

nitrogen-to-protein conversion factors of 3.99 for mushrooms, 4.39 for vegetables, 5.75

41

for rice, 5.81 for wheat, and 5.95 for other cereals. On the other hand, Diniz et al.11

42

calculated conversion factors of 5.39 to 5.98 for nine species of fish from the Brazilian

43

coast. There have also been many other reports12-14 demonstrating that the traditional

44

conversion factor (kP) of 6.25 based on the assumption that the nitrogen content of

45

proteins to be 16% is not suitable for estimating protein content in actual samples. In

46

addition, most reported conversion factors were inferred from food and feed

3

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

47

products,8-10,15-18 but rarely from biomass samples.12,19 Indeed, we know of very few

48

conversion factors for crop residues or animal manure.

49

Thus, in this study, we determined the amino acid composition, protein content, and

50

three types of nitrogen-to-protein conversion factors (kA, kP, and k) for five crop

51

residues and five types of animal manure. As defined by Mossé et al.,17 kA is the ratio of

52

total anhydrous amino acids to total amino acid nitrogen, kP is the ratio of total

53

anhydrous amino acids to total nitrogen, and k is the average of kA and kP. On the basis

54

of the differences in these values, we now recommend new k factors more suitable for

55

estimating protein content in crop residues and animal manure.

56 57

2. MATERIALS AND METHODS

58

2.1. Materials. A total of 50 representative crop residues, consisting of 10 samples

59

each of wheat straw, rice straw, corn stover, rape stalk, and cotton stalk, were collected

60

from different sites in China in 2011-2014. Each sample was collected at the fully ripe

61

stage, with the grain and root removed and only the middle part retained, and

62

thoroughly mixed to obtain a representative batch of approximately 2 kg. Subsequently,

63

samples were dried for 36-48 h at 45 °C in a forced-air drying oven, per American

64

Society for Testing and Materials E1757-01. Samples were then milled in a ZM100 mill

65

fitted with a 0.90-mm sieve (Retsch GmbH & Company, Germany), and stored in

66

plastic bags until analysis.20

67

Fifty specimens of animal manure were also obtained from a variety of sources,21

68

and consisted of 10 samples each of pig, dairy, beef, layer, and broiler manure. Each

69

sample was collected from different sites on the unit floor in each barn, and a

70

representative batch of about 2 kg was obtained after thorough mixing. The samples

71

were then dried in a forced-air drying oven at 70 ± 5 °C for 18-24 h until there was no 4

ACS Paragon Plus Environment

Page 4 of 25

Page 5 of 25

Journal of Agricultural and Food Chemistry

72

significant loss of moisture. After cooling, samples were directly ground in a ZM100

73

mill (Retsch GmbH & Company, Germany), and passed through a 0.5-mm sieve.

74

Finally, samples were stored in tightly sealed containers until analysis.21

75

2.2. Analysis. Total nitrogen was determined according to the Official Methods of

76

Analysis of AOAC International,22 using a Kjeltec 2300 auto-analyzer (FOSS Tecator

77

AB, Sweden). To quantify amino acids, samples were hydrolyzed in 6 N HCl at 120 °C

78

for 22 h, and analyzed by high performance liquid chromatography at 40 °C on an

79

Agilent 1100 (USA) chromatography system fitted with a quaternary pump, an

80

autosampler, a thermostatted column compartment, an online vacuum degasser, an

81

ultraviolet (UV) detector, and a reversed-phase column (Agilent Hypersil ODS, 250

82

mm × 4.0 mm × 5 µm). Tryptophan was determined by hydrolysis in Ba(OH)2 and

83

subsequent acidification with HCl.23 Asparagine and glutamine levels were measured

84

by assigning moles of amide nitrogen on a proportional basis to the moles of aspartic

85

acid and glutamic acid present.18 Proline was quantified at 262 nm on HPLC, while all

86

others

87

acetate:trimethylamine:tetrahydrofuran (500:0.11:2.5, v:v:v) as solvent A and 80.9 mM

88

sodium acetate:methanol:acetonitrile (1:2:2, v:v:v) as solvent B. Both solvents were

89

adjusted to pH 7.20 with acetic acid. Samples (10 µL) were eluted at 1.0 mL/min over a

90

gradient of 8-50 % B until 17 min, 50-100 % B until 20.1 min, and 0 % B until 24.0

91

min. To measure amide nitrogen, samples were hydrolyzed in 3 N HCl at 115 °C for 2

92

h, and titrated for liberated ammonia, as described for total nitrogen.24

were

quantified

at

338

nm,

using

5

ACS Paragon Plus Environment

27.6

mM

sodium

Journal of Agricultural and Food Chemistry

93

2.3. Data Processing and Analysis. Box charts in OriginPro 8.0 were used to

94

analyze amino acid composition and calculate nitrogen-to-protein conversion factors.

95

SPSS 17.0 was used for one-way analysis of variance.

96 97

3. RESULTS AND DISCUSSION

98

3.1. Amino Acid Composition. The amino acid composition of five crop residues

99

and five types of animal manure is presented in Figure 1 as mean of 10 samples each.

100

Glutamic acid (Glu) was the most abundant in all crop residues except cotton stalk, in

101

which aspartic acid (Asp) was the most abundant instead (Figure 1A and Table S1).

102

Similar trends were described by Lourenco et al. for tropical seaweeds.25 In rice straw

103

and corn stover, Glu represented 0.65 % and 0.64 % of the dry basis, respectively, in

104

line with data obtained for rice and corn, in which the amino acid represents 0.41-0.99 %

105

and 0.38-1.57 % of the dry basis, respectively.10,18 In wheat straw, Glu accounted for

106

0.55 %, a level lower than that typically found in wheat (1.00-1.97 %). Levels of

107

cysteine (Cys), methionine (Met), asparagine (Asn), and glutamine (Gln) were notably

108

low in all residues, and lower than in cereal products, in which these amino acids

109

comprised 0.26 %, 0.32 %, 0.39 %, and 1.70 % of the dry basis, respectively.10 Indeed,

110

multiple reports indicate that cereal10 and common food items18 are rich in Asn and

111

Gln, however, great variety was found in different species. According to the literature,

112

wheat had high Gln level but low Asn content,10 while banana showed less both Gln

113

and Asn,18 which was in line with the low Gln and Asn contents of our data. As 6

ACS Paragon Plus Environment

Page 6 of 25

Page 7 of 25

Journal of Agricultural and Food Chemistry

114

reported by Fujihara et al.,10 for rice, Glu was the predominant amino acid in rice straw,

115

although Gln was much less abundant in the latter.

116

Similar trends were observed in animal manure (Figure 1B and Table S2), except that

117

average alanine (Ala) content was lower. Glu, Arg, Leu, Asp, and Pro constituted over

118

half of total amino acids in dairy and beef manure. On the other hand, pig manure, layer

119

manure, and broiler manure, in which Asp and Glu were the major amino acids,

120

contained higher levels of Arg, Asp, and Gly compared to other manure types.

121

Interestingly, layer manure was particularly rich in Arg, which constituted more than

122

24 % of total amino acids. Finally, the concentration of most amino acids was relatively

123

higher in pig and broiler manure than in other manure types.

124

On average, Glu, Asp, Arg, and Leu constituted over 40 % of total amino acids in

125

five crop residues and five types of animal manure, as was observed in algal biomass

126

tested by Templeton and Laurens.19

127

3.2. Protein Content. Protein content, listed in Table 1 as total anhydrous amino

128

acids, ranged from 2.65 % of the dry basis in rape stalk to 3.98 % in cotton stalk. Of

129

note, these values are lower than those typical of cereal products,10,15,18,26 but consistent

130

with those of leaves in 90 plant species12 (Table 2). On the other hand, protein content

131

was strongly variable in animal manure, with mean values ranging from 6.07 % in dairy

132

manure to 10.24 % in broiler manure. Pairwise comparison showed that broiler manure

133

and layer manure were significantly richer in protein (10.24 ± 2.90 % and 9.84 ±

134

1.79 %, respectively) than dairy manure (6.07 ± 3.06 %). These differences are 7

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

135

probably due to multiple factors, including growth stage, animal diet, and housing27,28.

136

In any case, crop residues rich in protein are generally considered nutritionally useful as

137

animal feed. Indeed, corn stover is frequently used as feed.20 Moreover, proteins in both

138

crop residues and animal manure are essential to produce large amounts of ammonia

139

nitrogen and to stabilize the pH during anaerobic fermentation.3

140

The protein nitrogen fraction, calculated as amino acid nitrogen/total nitrogen

141

(Figure 2), averaged 74.22 % for crop residues and 71.80 % for animal manure, in line

142

with those of vegetables,9 algae,19 and plant leaves,12 although rape stalk (84 %) and

143

broiler manure (54 %) had exceptionally high and low protein nitrogen fractions,

144

respectively. However, protein nitrogen fractions were extremely low compared to

145

those of food (89 %)18 and cereal products (93 %).10

146

3.3. Nitrogen-to-Protein Conversion Factors. To determine protein content

147

conveniently and accurately, the following nitrogen-to-protein conversion factors were

148

calculated: kA, the ratio of protein to amino acid nitrogen,24 kP, the ratio of protein to

149

total nitrogen,16 and k, the average of kA and kP.17 Ideally, these conversion factors

150

should be independent of the protein or nitrogen content of biomass (Table 1).

151

3.3.1. kA. The mean value of kA ranged from 5.42 to 6.00, with average 5.72 ± 0.39

152

for five crop residues, in close agreement with the general conversion factor of 5.7 for

153

wheat,30 animal, and plant products.18 Although significant differences among crop

154

residues were not observed, kA was lower for crape stalk (5.42 ± 0.24) than for rice

155

straw (6.00 ± 0.35). kA was also generally lower in animal manure, ranging from 4.78 8

ACS Paragon Plus Environment

Page 8 of 25

Page 9 of 25

Journal of Agricultural and Food Chemistry

156

for layer manure to 5.36 for beef manure. On average, the kA value for animal manure

157

(5.16 ± 0.31) was similar to that for green algae (5.13 ± 0.39)23. Values were

158

comparable for dairy (5.33 ± 0.11) and beef manure (5.36 ± 0.09), but was lower for

159

layer manure (4.78 ± 0.43). Such differences in kA are likely due to differences in

160

amino acid composition.19 Strikingly, the kA we obtained for crop residues and animal

161

manure was far from the traditional factor of 6.25. Furthermore, we note that kA can not

162

be used to estimate the true protein content from total nitrogen, because it does not

163

consider nonprotein nitrogen.9,10

164

3.3.2. kP. The conversion factor kP is more useful in practice, since it enables direct

165

estimation of protein content from total Kjeldahl or combustion (Dumas) nitrogen. For

166

the five crop residues we tested, we obtained mean values ranging from 3.97 to 4.57,

167

with overall average 4.23 ± 1.06. Significant variability was also observed among

168

manure types, with average values ranging from 2.76 for broiler manure to 4.31 for

169

dairy manure and significantly lower in comparison to those for crop residues.

170

Importantly, the kP values we obtained were significantly lower than the traditional

171

conversion factor of 6.25 due to the presence of nonprotein nitrogen. Instead, these

172

values are similar to those calculated for microalgae (2.53-5.77),31-33 tropical plants

173

(3.7-5.0),34 and various vegetables and mushrooms (2.38-5.84).8,9 Higher values

174

between 4.74 and 6.26 have also been reported for cereal products, meat, fish, egg, and

175

edible insects.10,18,35

9

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

176

3.3.3. k. A mean factor (k) of the two main usual factors (kA and kP) has been

177

proposed as a good compromise because kA and kP are higher and lower than the true

178

factor.17 To improve reliability and comparisons of conversion factors among different

179

species, the conversion factor k was also calculated here. The k values for wheat straw

180

(4.94), corn stover (4.95), rape stalk (4.99), and cotton stalk (4.91) were similar to those

181

reported for wheat germ (4.99)36 and wheat bran (4.96)13. Mossé17 reported a k value of

182

5.1 for rice grains, which is close to that we obtained for rice straw (5.19). Interestingly,

183

mean k values were lower for animal manure (3.92-4.82) than for crop residues

184

(4.91-5.19), although variability was higher among the former.

185

3.3.4. Choice of Conversion Factor. The choice of conversion factor may

186

significantly impact the estimate of protein content in any sample (Figure 3). For

187

example, kA should be considered for purified proteins, which contain very low levels

188

of nonprotein nitrogen. On the other hand, kP may be more suitable for low-protein

189

sources that are also rich in nonprotein nitrogen,13,15,17 such as the biomass samples we

190

tested (Figure 2). However, kP values were significantly different (p < 0.05) between

191

livestock (pig, dairy, and beef) and poultry manure (layer and broiler) and also highly

192

variable (Figure 3D), with average values 4.11 ± 0.68 and 3.11 ± 0.87, respectively.

193

Therefore, consensus kP values of 4.11 and 3.11 are recommended for livestock and

194

poultry manure. Variability was also observed in kP values for five crop residues, but

195

not to a statistically significant extent (p > 0.05), with average 4.23 ± 1.06 (Figure 3C).

10

ACS Paragon Plus Environment

Page 10 of 25

Page 11 of 25

Journal of Agricultural and Food Chemistry

196

Accordingly, a kP of 4.23 may provide a reliable estimate of protein content in crop

197

residues.

198

3.4. Summary. The average protein content of five crop residues ranged from 2.65 %

199

to 3.98 %, in agreement with published data for plant leaves, but was lower than that

200

for cereal products. A large variation in protein content was observed in animal manure,

201

with values ranging from 6.07 % to 10.24 %. Nitrogen-to-protein conversion factors

202

based on amino acid nitrogen (kA) varied from 5.42 to 6.00 for crop residues and from

203

4.78 to 5.36 for animal manure, indicating that the general conversion factor of 6.25 is

204

not suitable for biomass samples. On the other hand, the more practical conversion

205

factor based on the proportion of total anhydrous amino acids to total nitrogen (kP)

206

ranged from 3.97 to 4.57 and from 2.76 to 4.31 for crop residues and animal manure,

207

respectively, and are much lower than the traditional factor of 6.25 due to the presence

208

of nonprotein nitrogen. Hence, kP values of 4.23 for crop residues, 4.11 for livestock

209

manure, and 3.11 for poultry manure are recommended to reliably estimate biomass

210

protein from total nitrogen. These conversion factors should provide a quick and

211

reasonably accurate method of estimating the protein content in crop residues and

212

animal manure, and should facilitate their efficient use as feed or fuel.

213 214

ASSOCIATED CONTENT

215

Supporting Information

11

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

216

Table S1. Amino Acid Composition and Total Amino Acid Content (g/100 g Dry

217

Basis) of Crop Residues

218

Table S2. Amino Acid Composition and Total Amino Acid Content (g/100 g Dry

219

Basis) of Animal Manure

220 221

AUTHOR INFORMATION

222

Funding

223

We acknowledge the National Key R&D Program of China (No. 2016YFE0112800), the

224

European Union’s Horizon 2020 Research and Innovation Programme (No. 690142),

225

Project AgroCycle (Sustainable Techno-Economic Solutions for the Agricultural Value

226

Chain), and National Natural Science Foundation of China (No. 31671572).

227

Notes

228

The authors declare no competing financial interest.

229 230

ABBREVIATIONS USED

231

kA, ratio of anhydrous amino acids to amino acid nitrogen; kP, ratio of anhydrous amino

232

acids to total nitrogen; k, average of kA and kP.

12

ACS Paragon Plus Environment

Page 12 of 25

Page 13 of 25

Journal of Agricultural and Food Chemistry

233 234 235

REFERENCES (1) Deng, Y. Y.; Koper, M.; Haigh, M.; Dornburg, V. Country-level assessment of long-term global bioenergy potential. Biomass Bioenergy 2015, 74, 253-267.

236

(2) Huang Y, Dong H, Shang B, Xin H, Zhu Z. Characterization of animal manure

237

and cornstalk ashes as affected by incineration temperature. Appl Energy 2011, 88,

238

947–52.

239

(3) Ehimen, E. A.; Sun, Z. F.; Carrington, C. G.; Birch, E. J.; Eaton-Rye, J. J.

240

Anaerobic digestion of microalgae residues resulting from the biodiesel production

241

process. Appl. Energy 2011, 88, 3454-3463.

242 243

(4) Bagley, C. P.; Evans, R. R.; Burdine, W. B. Jr. Broiler litter as a fertilizer or livestock feed. J. Prod. Agric. 1996, 9, 342-346.

244

(5) El Jalil, M. H.; Faid, M.; Elyachioui, M. A biotechnological process for

245

treatment and recycling poultry wastes manure as a feed ingredient. Biomass Bioenergy

246

2001, 21, 301-309.

247 248

(6) Pugh, D. G.; Rankins, D. L.; Jr, Powe, T.; D'Andrea G. Feeding broiler litter to beef cattle. Vet. Med. 1994, 89, 661-664.

249

(7) Moore, J. C.; Devries, J. W.; Lipp, M.; Griffiths, J. C.; Abernethy, D. R. Total

250

protein methods and their potential utility to reduce the risk of food protein

251

adulteration. Compr. Rev. Food Sci. Food Saf. 2010, 9, 330-357.

13

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

252

(8) Fujihara, S.; Kasuga, A.; Aoyagi, Y.; Sugahara, T. Nitrogen-to-protein

253

conversion factors for some common edible mushrooms. J. Food Sci. 1995, 60,

254

1045-1047.

255 256

(9) Fujihara, S.; Kasuga, A.; Aoyagi, Y. Nitrogen-to-protein conversion factors for common vegetables in Japan. J. Food Sci. 2001, 66, 412-415.

257

(10) Fujihara, S.; Sasaki, H.; Aoyagi, Y.; Sugahara, T. Nitrogen-to-protein

258

conversion factors for some cereal products in Japan. J. Food Sci. 2008, 73,

259

C204-C209.

260

(11) Diniz, G. S.; Barbarino, E.; Oiano-Neto, J.; Pacheco, S.; Lourenço, S. O.

261

Gross chemical profile and calculation of nitrogen-to-protein conversion factors for

262

nine species of fishes from coastal waters of Brazil. Lat. Am. J. Aquat. Res. 2013, 41,

263

254-264.

264 265 266 267

(12) Yeoh, H. H.; Wee, Y. C. Leaf protein contents and nitrogen-to-protein conversion factors for 90 plant species. Food Chem. 1994, 49, 245-250. (13) Mariotti, F.; Tomé, D.; Mirand, P. P. Converting nitrogen into protein--beyond 6.25 and Jones' factors. Crit. Rev. Food Sci. Nutr. 2008, 48, 177-184.

268

(14) Maclean, W.; Harnly, J., Chen, J.; Chevassus-Agnes, S.; Gilani, G.; Livesey,

269

G.; Warwick, P. Food energy–Methods of analysis and conversion factors. Food and

270

Agriculture Organization of the United Nations Technical Workshop Report, Rome,

271

2003.

14

ACS Paragon Plus Environment

Page 14 of 25

Page 15 of 25

Journal of Agricultural and Food Chemistry

272 273 274 275

(15) Jones, D. B. Factors for converting percentages of nitrogen in foods and feeds into percentages of proteins. USDA Circ. 1931, 183, 1-22. (16) Sosulski, F. W.; Holt, N. W. Amino acid composition and nitrogen-to-protein factors for grain legumes. Can. J. Plant Sci. 1980, 60, 1327-1331.

276

(17) Mosse, J. Nitrogen-to-protein conversion factor for ten cereals and six

277

legumes or oilseeds. A reappraisal of its definition and determination. Variation

278

according to species and to seed protein content. J. Agric. Food Chem. 1990, 38, 18-24.

279

(18) Sosulski, F. W.; Imafidon, G. I. Amino acid composition and

280

nitrogen-to-protein conversion factors for animal and plant foods. J. Agric. Food Chem.

281

1990, 38, 1351-1356.

282

(19) Templeton, D. W.; Laurens, L. M. L. Nitrogen-to-protein conversion factors

283

revisited for applications of microalgal biomass conversion to food, feed and fuel. Algal

284

Res. 2015, 11, 359-367.

285

(20) Niu, W.; Han, L.; Liu, X.; Huang, G.; Chen, L.; Xiao, W.; Yang, Z.

286

Twenty-two compositional characterizations and theoretical energy potentials of

287

extensively diversified China's crop residues. Energy 2016, 100, 238-250.

288

(21) Shen, X.; Huang, G.; Yang, Z.; Han, L. Compositional characteristics and

289

energy potential of Chinese animal manure by type and as a whole. Appl. Energy 2015,

290

160, 108-119.

15

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

291

(22)

Horwitz, W.; Latimer G. AOAC Official Method 2001.11 Protein (crude)

292

inanimal feed, forafe (plant tissue), grain and oilseeds. Official Methods of Analysis of

293

AOAC International, 2009.

294

(23) Sriperm, N.; Pesti, G. M.; Tillman, P. B. The distribution of crude protein and

295

amino acid content in maize grain and soybean meal. Anim. Feed Sci. Technol. 2010,

296

159, 131-137.

297 298

(24) Mossé, J.; Huet, J. C.; Baudet, J. The amino acid composition of wheat grain as a function of nitrogen content. J. Cereal Sci. 1985, 3, 115-130.

299

(25) Lourenço, S. O.; Barbarino, E.; De-Paula, J. C.; da S. Pereira, L. O.; Lanfer

300

Marquez, U. M. Amino acid composition, protein content and calculation of

301

nitrogen-to-protein conversion factors for 19 tropical seaweeds. Phycol. Res. 2002, 50,

302

233-241.

303

(26) Sriperm, N.; Pesti, G. M.; Tillman, P. B. Evaluation of the fixed

304

nitrogen-to-protein (N:P) conversion factor (6.25) versus ingredient specific N:P

305

conversion factors in feedstuffs. J. Sci. Food Agric. 2011, 91, 1182-1186.

306

(27) Suresh, A.; Choi, H. L. Estimation of nutrients and organic matter in Korean

307

swine slurry using multiple regression analysis of physical and chemical properties.

308

Bioresour. Technol. 2011, 102, 8848-8859.

309

(28) Suresh, A.; Choi, H. L.; Oh, D. I.; Moon, O. K. Prediction of the nutrients

310

value and biochemical characteristics of swine slurry by measurement of EC–electrical

311

conductivity. Bioresour. Technol. 2009, 100, 4683-4689. 16

ACS Paragon Plus Environment

Page 16 of 25

Page 17 of 25

Journal of Agricultural and Food Chemistry

312 313 314 315

(29) Yeoh, H. H.; Watson, L. Taxonomic variation in total leaf protein amino acid compositions of grasses. Phytochemistry 1982, 21, 615-626. (30) Teller, G. Non-protein nitrogen compounds in cereals and their relation to the nitrogen factor for protein in cereals and bread. Cereal Chem. 1932, 9, 261-274.

316

(31) Lourenço, S. O.; Barbarino, E.; Lanfer Marquez, U. M.; Aidar, E. Distribution

317

of intracellular nitrogen in marine microalgae: calculation of new nitrogen-to-protein

318

conversion factors. Eur. J. Phycol. 2004, 39, 17-32.

319

(32) Schwenzfeier, A.; Wierenga, P. A.; Gruppen, H. Isolation and characterization

320

of soluble protein from the green microalgae Tetraselmis sp. Bioresour. Technol. 2011,

321

102, 9121-9127.

322

(33) Gilbert-López, B.; Mendiola, J. A.; Fontecha, J.; van den Broek, L. A.;

323

Sijtsma, L.; Cifuentes, A.; Herrero, M.; Ibañez, E. Downstream processing of

324

Isochrysis galbana: a step towards microalgal biorefinery. Green Chem. 2015, 17,

325

4599-4609.

326 327

(34) Milton, K.; Dintzis, F. R. Nitrogen-to-protein conversion factors for tropical plant samples. Biotropica 1981, 13, 177-181.

328

(35) Janssen, R. H.; Vincken, J. P.; van den Broek, L. A.; Fogliano, V.; Lakemond,

329

C. M. Nitrogen-to-protein conversion factors for three edible insects: Tenebrio molitor,

330

Alphitobius diaperinus, and Hermetia illucens. J. Agric. Food Chem. 2017, 65,

331

2275-2278.

17

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

332 333

(36) Tkachuk, R. Nitrogen-to-protein conversion factors for cereals and oil-seed meals. Cereal Chem. 1969, 46, 419-423.

18

ACS Paragon Plus Environment

Page 18 of 25

Page 19 of 25

Journal of Agricultural and Food Chemistry

334

FIGURE CAPTIONS

335

Figure 1. The averaged value of each amino acid for (A) five crop residues; (B) five

336

types of animal manure. All data are shown as % contribution to weight of dry basis.

337

Figure 2. Protein nitrogen fraction in biomass tested in this and previous studies (*

338

mushroom,8 vegetables,9 algal samples,19 plant leaves,12 food products,18 and cereal

339

products10).

340

Figure 3. Variability in kA (A,B), kP (C,D) and k (E,F) for crop residues (A,C,E) and

341

animal manure (B,D,F). Middle lines and hollow squares within the box mark the

342

median and mean, respectively, and the lower and upper boundaries represent the 25th

343

and 75th percentile. Error bars above and below the box indicate 90 and 10 percentiles

344

of all data, while diamonds inside and outside the box are > 90 and < 10 percentiles.

345

19

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 20 of 25

TABLES

Table 1. Protein Content and Nitrogen-to-Protein Conversion Factor for Crop Residues and Animal Manurea Proteinb

nitrogen recovery

nitrogen-to-protein conversion factorsc

(wt% of dry basis)

samples

sample

(wt% of dry size

Kjeldahl basis)

amino acids

kA

kP

k

0.76 ± 0.44

5.78 ± 0.43

4.10 ± 0.59

4.94 ± 0.40

10

nitrogen crop residues wheat straw

3.12 ± 1.84

0.53 ± 0.28

rice straw

3.84 ± 0.95

0.65 ± 0.19

0.89 ± 0.22

6.00 ± 0.35

4.37 ± 0.59

5.19 ± 0.26

10

corn stover

3.50 ± 0.81

0.61 ± 0.15

0.89 ± 0.23

5.72 ± 0.38

3.97 ± 0.54

4.95 ± 0.32

10

rape stalk

2.65 ± 1.02

0.49 ± 0.19

0.62 ± 0.29

5.42 ± 0.24

4.57 ± 1.19

4.99 ± 0.69

10

cotton stalk

3.98 ± 1.63

0.71 ± 0.29

1.00 ± 0.20

5.68 ± 0.37

4.13 ± 1.88

4.91 ± 0.91

10

total sample

3.42 ± 1.35

0.60 ± 0.23

0.83 ± 0.31

5.72 ± 0.39

4.23 ± 1.06

4.97 ± 0.56

50

pig manure

9.19 ± 3.25

1.74 ± 0.61

2.27 ± 0.75

5.28 ± 0.07

4.04 ± 0.43

4.66 ± 0.23

10

dairy manure

6.07 ± 3.06

1.13 ± 0.55

1.47 ± 0.74

5.33 ± 0.11

4.31 ± 0.97

4.82 ± 0.51

10

beef manure

7.72 ± 1.77

1.44 ± 0.33

1.94 ± 0.37

5.36 ± 0.09

3.99 ± 0.56

4.67 ± 0.29

10

layer manure

9.84 ± 1.79

2.09 ± 0.48

2.94 ± 0.68

4.78 ± 0.43

3.45 ± 0.72

4.11 ± 0.38

10

broiler manure

10.24 ± 2.90

2.03 ± 0.60

4.10 ± 1.44

5.08 ± 0.20

2.76 ± 0.90

3.92 ± 0.50

10

total sample

8.61 ± 2.96

1.69 ± 0.62

2.54 ± 1.24

5.16 ± 0.31

3.71 ±0.90

4.44 ± 0.52

50

animal manure

a

b

The results are recorded as the mean ± standard deviation. Sum of anhydrous amino acids, and represents the true protein

content. ckA is the ratio of protein to amino acid nitrogen; kP is the ratio of protein to total Kjeldahl nitrogen; k is the average of kA and kP.

20

ACS Paragon Plus Environment

Page 21 of 25

Journal of Agricultural and Food Chemistry

Table 2. Reported Protein Content of Common Cereal Products and Plant Leaves samples

protein content (wt% of dry basis)

reference

wheat

8.46 – 14.10

10,15,18

rice

4.82 – 8.06

10,18

corn

5.30 – 8.61

10,18,26

plant leaves

0.20 – 7.45

12,29

21

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 22 of 25

FIGURES

% weight of dry basis

A

0.7

Wheat straw Rice straw Corn stover Rape stalk Cotton stalk

0.6 0.5 0.4 0.3 0.2 0.1 0.0

Ala Arg Asp Cys Glu Gly His

Ile

Leu Lys Met Phe Pro Ser Thr Trp Tyr Val Asn Gln

% weight of dry basis

B 3.0 Pig manure Dairy manure Beef manure Layer manure Broiler manure

2.5 2.0 1.5 1.0 0.5 0.0

Ala Arg Asp Cys Glu Gly His

Ile

Leu Lys Met Phe Pro Ser Thr Trp Tyr Val Asn Gln

Figure 1

22

ACS Paragon Plus Environment

Page 23 of 25

Journal of Agricultural and Food Chemistry

Protein nitrogen fraction

Nonprotein nitrogen fraction

100% 80% 60% 40% 20% 0%

Figure 2

23

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Figure 3

24

ACS Paragon Plus Environment

Page 24 of 25

Page 25 of 25

Journal of Agricultural and Food Chemistry

TOC GRAPHIC

25

ACS Paragon Plus Environment