J Sci Food Agric 1996,71, 151-155

High Lysine Extruded Products of Quality Protein Maize B F Martinez,* J D C Figueroa and S A Larios Centro de Investigacion y de Estudios Avanzados del Instituto Politecnico Nacional, Dpto de Biotecnologia y Bioingenieria, Alimentos y Laboratorio de Materiales Avanzados, Facultad de Quimica-CINVESTAV Cerro de las Campanas, Universidad Autonoma de Queretaro, CP 76010, Queretaro, Qro. Mexico

(Received 29 August 1994; revised version received 20 June 1995; accepted 27 November 1995)

Abstract: Extrusion-cooking is used by several food industries to produce expanded snack foods, ready-to-eat cereals and pet foods from corn meal. A snack food utilising normal maize and quality protein maize (QPM) as its main ingredient was developed and characterised. The extrusion process was per- formed in a Mapimpianti single cooker extruder. Processing conditions were single screw with a screw speed of 150 rpm, and a die with 20 die-nozzle orifices with openings of 2 mm of diameter. The die head zone was heated at 110°C by electrical resistance. Compressed air was circulated around the barrel to main- tain precise control of the temperature. Moisture content of samples were 150 and 200 g kg-'. The extruded products showed low density and high expansion degree. Optimum expansion index was obtained with flours processed at 150 g kg-' of moisture content in both maize samples with better characteristics for QPM extrudates. The white colour values were highest for QPM compared to H-128 extruded products.

Key words: quality protein maize (QPM), normal maize, maize/corn, high lysine, extrusion, extruded products.

INTRODUCTION Maize meal is a major ingredient of expanded snack foods, ready-to-eat-cereals, and dry pet foods, those

The search for maize genotypes with enhanced nutri- manufactured by high-temperature short-time extrusion tional quality led to identification of Opaque-2 (02) as cooking. The objective of this research was to compare potentially useful mutations for increasing the lysine the extrusion properties and nutritional quality of and tryptophan contents of the grain (Mertz et a1 1964). QPM with normal maize hybrid.

In improving protein quality of normal maize endo- sperm of 0 2 gene, initially soft 0 2 varieties were devel- oped. These unfortunately suffer from the problem of EXPERIMENTAL

low grain yield, kernel phenotype, drying ability, ear rots, and storage grain pests (Villegas et al 1990).

Agricultural scientists from the International Maize and Wheat Improvement Center (CIMMYT) bred modified 0 2 into genotypes with a high frequency of 'modifier genes' that confer a normal, vitreous pheno-

The maize samples used in this study were QPM experi- mental white hybrid grown at Poza Rica (CIMMYT, Experimental Station), Veracruz, Mexico in 1991. H-128 white commercial hybrid maize was grown at Chapingo Mexico in 1992.

type to the endosperm, while maintaining high levels of lysine and tryptophan in the protein and similar to normal maize in agronomic characters (Bjarnason and Vasal 1992).

* To whom correspondence should be addressed.

J Sci Food Agric 0022-5142/96/$09.00 0 1996 SCI. Printed in Great Britain

Preparation Of samples and extrusion process

Grits samples were ground (particle size 350 pm), using a Wiley mill, and conditioned at 150 and 200 g kg-' moisture content during 12 h. The flours were extruded

151

152 B F Martinez, J D C Figueroa, S A Larios

in a Mapimpianti single screw cooker-extruder. Flour samples were fed by a forced feeding, variable-speed and maintained at 70 g (dry matter) min- l. A screw speed of 150 rpm, a die with 20 die-nozzle orifices with openings of 2 mm of diameter were used. The die head zone was heated at 110°C by electrical resistance. Compressed air was circulated around the barrel to maintain precise control of the temperature.

Analysis

Moisture, protein (N x 6-25), fat (ether extract), starch and ash contents were determined using standard AACC (1986) procedures. Insoluble and soluble dietary fibre were determined according to the method of Englyst and Cummings (1988), and lysine analysis was carried out following the procedure of Spackman et a1 (1958).

Water absorption index (WAI) and water solublity index (WSI)

Water absorption (WAI) and water solubility (WSI) indexes were determined as described by Anderson et al. (1969).

Expansion and density

Expansion ratio was calculated by dividing the average cross-sectional area of the extrudate by the cross- sectional area of the extruder die-nozzle orifice. Density was calculated by weighing pieces of extruded products and measuring their length and average diameter, then calculated as follows :

4 x m 3.14 x dZ x h

b =

where b is the density (gcm-'); m is the mass of a sample (g); d is the diameter of a sample (cm); and h is the length of a sample (cm) (Chinnaswamy and Hanna 1988).

Colour

Colour was determined with a Hunter Lab reflectance colour.

Statistical analysis

Analysis were carried out using a random design with a factorial arrangement 2 x 2 x 3, under 12 treatments consisting of two factors (QPM and H-128 corn), two levels of moisture content (150 and 200 g kg-I), and three repetitions. The data were analysed by using Sta- tistical Analysis System (SAS 1985). Duncan analysis (P c 0.05) was applied to means with significant differ- ences.

RESULTS AND DISCUSSION

Chemical composition

Interactions of plant genotype and environment condi- tions determine the chemical composition of maize. Results of several analytical procedures applied to raw QPM, and H-128 maize hybrids and their respective extrudates processed at 150 and 200 g kg-' moisture content, are presented in Tables 1, 2, 3 and 4. QPM showed higher amounts of protein than normal maize and also better protein quality than the normal maize due to a higher lysine content. High lysine mutants have reduced levels of zein fraction and increased levels of albumins, globulins and glutelins (Misra et a1 1975). Starch is the major component of maize. QPM had the lowest amount of starch. Starch content varies inversely with the protein content of endosperm (Freedman 1973). Lawton et a1 (1972) investigated the chemical and physical changes that occurred in an extruded corn starch product due to extruder variables. These researches found that moisture and barrel temperature had the greatest effect on gelatinisation of corn starch. Gomez and Aguilera (1983) developed a physi- cochemical model for extrusion cooking of corn starch,

TABLE 1 Chemical composition (dry basis) of maize samples extruded at 150 g kg-' mois-

ture content"

105.6a 826.5b 15.1a 35.6a 17.2a 14.lb

QPM Extruded QPM 106.0a 831.0b 14-lb 34.1a H-128 104.4a 842.2a 13.8b 26.6b 12.8~ Extruded H-128 105sOa 845.0a 14.0b 2 4 . 6 ~ 12*0d

Values with the same following letter are not significantly different within each column at P < 0.05.

High lysine extruded products of quality protein maize 153

TABLE 2 Physical characteristics of maize samples extruded at 150 g kg- moisture content'

Flour corn W A l b WSIb Db Colour samples ( g / d (9 kg - ' 1 (9 cm - 7

L a b

QPM 1 . 6 ~ 62c - 79.9a -0.35a 10.8a Extruded QPM 5.9a 321a 1.7a 77.9b -0.45a 10.7a H- 128 1 . 6 ~ 79b - 76.1~ -0.15b 10.5a Extruded H-128 50b 320a 1.5a 73.5d -1.7b 10.1a

a Values with the same following letter are not significantly different within each column at P < 0.05.

WAI, water absorption index; WSI, water solubility index; D, density

indicating that dextrinisation predominates at moisture contents below 200 g kg- ', whereas gelatinisation pre- dominates at moisture contents above 200 g kg- '.

Lysine content of QPM and H-128 normal maize was decreased significantly during the extrusion process. However, QPM extrudates showed better lysine content in comparison to H-128 extruded maize samples (Fig 1).

Tables 1 and 3 shows that QPM presented a higher amount of fat than the normal maize. This is because germ size was increased for the QPM hybrids and the proportion of endcisperm was reduced. QPM showed higher amount of total dietary fibre and ash compared

to H- 128. No significant differences were found in the protein content of extruded products in comparison to raw materials processed at 150 and 200 g kg-' mois- ture content. QPM extrudates had the lowest starch content. QPM extrudates contained a higher content of dietary fibre and ash than H-128 extrudates.

WAI and WSI

All extruded samples showed physical characteristics significantly different from those of the raw material,

TABLE 3 Proximate composition (dry basis) of maize samples extruded at 200 g kg- ' mois-

ture content"

Flour corn Protein Starch Ash Fat Dietary samples (9 b-') (9 k - ' ) (9 k g - ' ) (9 k g - 7 fibre

(9 k g - '1 100.4a 817.4~ 16.0a 39.3a 16.7a

14.0b Extruded QPM 110.6a 822.7d 16.la 36.5b H-128 105.0a 842.3a 13.7b 27.3~ 11.6~ Extruded H-128 106.0a 854.5b 14.0b 24.6d 10.7d

QPM

a Values with the same following letter are not significantly different within each column at P < 0.05.

TABLE 4 Physical characteristics of maize samples extruded at 200 g kg- ' moisture content"

'QPM 1 *6c 62d - 79.4a -0.2a 12.8a Extruded QPM 74a 173a 1.8a 78.6b -0.5a 12.8a H-128 1 . 6 ~ 79c - 7 7 . 2 ~ -1'2b 10'3b ]Extruded H-128 7.2b 170b 1.6a 73.7d -1.3b 10.0~

' Values with the same following letter are not significantly different within each clolumn at P < 0.05.

WAI, water absorption index; WSI water solubility index; D, density.

154

50

40

C .A

P) U

e 30 -

I

m x CII

.A 5 20 x

10

0

B F Martinez, J D C Figueroa, S A Larios

- ~

1 I I 4

QPM QPM* H-128 H-128. QPM QPM+ H-128 H-128+

Fig 1. Lysine content of flours and extrudates (* 150, + 200 moisture content g kg- ' before extrusion).

and denoted changes in the state of the main chemical components. Water absorption depends on the avail- ability of hydrophilic groups that bind water molecules and on the gel-forming capacity of macromolecules. WAI and WSI were low for raw maize flours and maximum for extruded products. The highest values of WAI were obtained with flours extruded at 200 g kg-' moisture content (Tables 2 and 4).

Expansion and density

Expanded volume of cereals and ,starches is generally governed by extrusion cooking parameters such as barrel temperature, screw speed, diameter of the die

nozzle orifice, and moisture content of the fed material (Anderson et a1 1969; Mercier and Feillet 1975), as well as the protein (Faubion and Hoseney 1982), lipid (Colonna et aE 1983), and starch (Anderson et a1 1969; Mercier and Feillet 1975) composition of the feed materials. The expansion ratio of the QPM, and H-128 extruded at 150 g kg-' moisture content (3.7 and 3.5, respectively) were higher than the same samples extruded at 200 g kg-' moisture content (3.6 and 2.9, respectively), with better values for QPM extrudates (Fig 2). As moisture content of the sample decreased, gelatinisation was complete, resulting in more expan- sion and reduced density. The expanded samples showed an increase in volume as the extent of gelati- nisation increased. Extruded products with a low

4

3

C 0 -4

m

5 2 t

1

0

n

QPM* H-128. QPM+ H-128*

Fig 2. Expansion of extrudates (* 150, +200 moisture content g kg- ', before extrusion).

High lysine ex truded products of qual i ty protein maize 155

amount of gelatinisation were crispy after puffing. The highly gelatinised extruded products with 150 g kg-’ moisture content were larger in volume and less dense. Mercier (1977) reported similar findings for directly expanded and extruded potato starch.

Extruded maize flours processed at 150 g kg-’ mois- ture content show values of WAI highly significant cor- related with expansion ( r = 0.99, P < 0-05), and significantly negative correlated with density ( r = -0.93, 1’ < 0.05).

Colour

Mean Hunter Color Meter values indicated that the white (‘L’) colour values were decreased significantly ( P > 0.05) during the extrusion process suggesting browning reactions. The white colour values were highest t o QPM compared to H-128 extruded products.

CONCLUSIONS

The characteristics of expansion index, water absorp- tion index and colour (‘~2‘) showed significantly higher values for QPM than those of H-128 extruded products.

QPM and H-128 extruded at 150 g kg-’ moisture content had higher expansion and lower density than the same samples extruded at 200 g kg-‘ moisture content with better expansion and lower density for QPM extrudates.

The higher lysine content of QPM extrudates could substantially raise the nutritional quality of these pro- ducts, suggesting that QPM may advantageously replace regular maize in extruded products.

REFERENCES

AACC 1986 .4pproved Methods. American Association of Cereal Chemists, St Paul, MN, USA.

Anderson R A, Conway H F, Pfeifer V F, Grifin E L J r 1969 Gelatinization of corn grits by roll and extrusion cooking. Cereal Sci Today 14 1-4.

Bjarnason M, Vasal S 1992 Breeding of quality protein maize (QPM). Plant Breeding Rev 9 181-216.

Chinnaswamy R, Hanna M A 1988 Relationship between amylose content and extrusion-expansion properties of corn starches. Cereal Chem 65 138-143.

Colonna P, Melcion J P, Vergnes B, Mercier C 1983 Flow mixing and residence time distribution of maize starch within a twin-screw extruder with a longitudinally-split barrel. J Cereal Sci 1 115-125.

Englyst H N, Cummings J H 1988 An improved method for measurement of dietary fibre as the non-starch poly- saccharides in plant foods. JAOAC 71 808-814.

Faubion J M, Hoseney R C 1982 High-temperature short- time extrusion cooking of wheat starch and flour. I. Effect of moisture and flour type on extrudate properties. Cereal Chem 59 529-533.

Freedman J E 1973 Quality factors affecting value of corn for wet milling. Trans ASAE 16 671-679.

Gomez M H, Aguilera J M 1983 Changes in the starch frac- tion during extrusion-cooking of corn. J Food Sci 48 378- 381.

Lawton B T, Henderson G A, Derlakta E J 1972 The effects of extruder variables on the gelatinization of corn starch. Can J Chem Engng 50 168-1 72.

Mercier C, Feillet P 1975 Modification of carbohydrate com- ponents by extrusion cooking of cereal products. Cereal Chem 52 283-297.

Mercier C 1977 Effects of extrusion-cooking on potato starch using twin screw french extruder. Staerke 29 48-52.

Mertz E T, Bates L S, Nelson 0 E 1964 Mutant gene that changes protein composition and increases lysine content of maize endosperm. Science 145 279-280.

Misra P S, Mertz E T, Glover D V 1975 Studies on corn proteins. Endosperm changes in single and double endo- sperm mutants of maize. Cereal Chem 52, 161-166.

SAS 1985 User’s Guide: Statistics (Version 5 edition). SAS Institute Inc, Cary, NC, USA.

Spackman D H, Stein W H H, Moore S 1958 Automatic recording apparatus for use in chromatography of amino acids. Anal Chem 30 1190.

Villegas E, Vasal S, Bjarnason M 1990 Quality protein maize-What is it and how was i t developed? Presented at the Quality Protein Maize (QPM) Symposium. Am Assoc Cereal Chem Annual Meeting, 14-18 October, Dallas, TX, USA.