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Influence of processing variables during micronization of wheat on starch structure and subsequent performance and digestibility in weaned piglets fed wheat-based diets
Animal Feed Science and Technology 93 (2001) 93±107
In¯uence of processing variables during micronization of wheat on starch structure and subsequent performance and digestibility in weaned piglets fed wheat-based diets L.N. Zarkadas1, J. Wiseman* Division of Agriculture and Horticulture, School of BioSciences, University of Nottingham, Sutton Bonington Campus, Loughborough, Leics, LE12 5RD, UK Received 21 February 2000; received in revised form 13 March 2001; accepted 29 March 2001
Abstract Physical and nutritional characteristics of wheat following micronization were determined in three experiments, each based on four treatments with four gilts and four entire males (from 10 to 27 kg liveweight) per treatment all using the same batch of wheat, designed to investigate the effect of temperatures (different heating time, Trials 1 and 2) and preconditioning (steeping the grains for different lengths of time) prior to different micronization temperatures (Trial 3). Micronization of wheat reduced crystallinity, as detected through X-ray diffractogram analysis, and increased gelatinized starch and viscosity in vitro particularly when preconditioned. Coef®cients of total tract apparent digestibilities (CTTAD) of dry matter (DM), gross energy (GE) and nitrogen (N) of diets containing wheat were not signi®cantly different between treatments (Trial 1) neither was daily liveweight gain (DLWG). Diets containing raw wheat had signi®cantly better (P 0:013) feed conversion ratio (FCR). Similar responses were obtained in Trial 2 suggesting limited effect of storage time prior to micronization. The in¯uence of preconditioning (2 and 12 h steeping time) followed by low and high cook conditions was examined in Trial 3. Signi®cant improvements for the shorter versus longer steeping time for DLWG (536 versus 484 g per day, P 0:007), feed intake (FI, 796 versus 735 g DM per day, P < 0:001), CTTAD for DM (0.838 versus 0.812, P 0:006) and GE (0.828 versus 0.802, P 0:010) were observed, while interaction of steeping time temperature was signi®cant for FCR (P 0:029). No effect of heating time was observed. There were no correlations between animal responses within individual trials and wheat starch crystallinity or viscosity (in vitro assessments). In conclusion, the addition of wheat micronized
* Corresponding author. Tel.: 44-115-9516054; fax: 44-115-9516060. E-mail address: [email protected] (J. Wiseman). 1 Co-corresponding author.
0377-8401/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 7 - 8 4 0 1 ( 0 1 ) 0 0 2 6 6 - 8
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under different conditions did not improve piglet performance although pre-conditioning did have an effect. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Micronization; Wheat; Starch; Gelatinization; Piglet; Digestibility; Performance
1. Introduction Processing applied to feedstuffs is both expensive and time-consuming and would not be undertaken unless it offered advantages, both biological and economic. Cold/hot, dry/wet, mechanical and chemical methods of treatment may be used, with the objectives of improving palatability (promoting feed intake (FI)), avoiding wastage and enhancing performance. Other objectives would be to improve digestibility and/or nutritive value (Champ and Delort-Laval, 1991), to prevent spoilage and inactivate heat labile antinutritional factors. Heat treatment of cereals alters kernel structure, thus, enhancing release of starch granules from the protein matrix and disrupting their order during gelatinization (i.e. degree of crystallinity) resulting in increased susceptibility to enzyme activity (Hoover and Vasanthan, 1994) which should increase carbohydrate utilization. Micronization is a short time high temperature cooking process using moisture, temperature and mechanical pressure to achieve conditions for optimum cooking and starch gelatinization (Lawrence, 1973a). Grains are preconditioned to increase moisture content and are heated on a vibrating bed under a radiant heat source (gas heaters, which emit energy principally in the infrared region of the electromagnetic spectrum) for a speci®c time depending on the product and then ¯aked. Performance of growing ®nishing pigs has been shown to be improved following micronization of cereals (Lawrence, 1973a) associated with increased digestibility of diet dry matter (DM), gross energy (GE) (Lawrence, 1973b) and amino acids (Huang et al., 1997). Many studies have evaluated the effects of processing which, however, tend to be limited to a consideration of a named process only. There are a number of variables associated with each process whose nutritional consequences have not been widely studied making conclusions on the effect of processing dif®cult to draw. The objective of the current programme was to investigate the effect of different micronization temperatures of wheat as well as the effect of pre-conditioning the grain prior to heat treatment at known temperatures on physico-chemical characteristics and on performance and digestibility when included in diets for weaned piglets (10±27 kg). 2. Experimental 2.1. Animals, housing and management All three experiments were conducted similarly based on the same batch of wheat. A total of 32 piglets (16 of each sex) from the University of Nottingham herd (commercial white hybrid) weaned between 24 and 25 days of age (8±10 kg) were employed for each
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trial. Animals were individually weighed, transferred to an environmentally controlled room (experimental unit), housed in individual pens with semi slatted ¯oors, two nipple drinkers and a feed trough. A commercial weaner diet was offered twice daily, at 08.30 and 17.00 h during the acclimatization period (6±7 days) at the end of which piglets were weighed and randomly allocated to one of four experimental diets which were offered on a restricted basis, 0.95 of assumed ad libitum intake, in relation to live weight. At feeding, diets were mixed in the approximate proportions water:food 2:1 to avoid dust and spillage. Water was also available ad libitum. Any feed wasted was removed, dried, weighed and a sample retained for DM determination. Liveweight and FI were determined weekly and the trial concluded when animals reached 27 kg liveweight. 2.2. Digestibility study Digestibility of each experimental diet was determined using four pigs per diet once a pig had reached a liveweight of 15 kg. Each meal allowance during the digestibility study contained the inert marker titanium dioxide (TiO2) at a rate of 1 g/kg diet and was fed for 5 days. Following that, the grills on the ¯oor of each cage were cleaned thoroughly following the morning feed and diets were fed for an additional 5 days during a collection period during which, on each day, a fresh faecal sample was removed from each pen at regular intervals during the day (animals were checked every 2 h) and stored in a plastic bag, for each pig, at 208C immediately after each collection. The grills of each ¯oor were cleaned daily after the morning feed. Faecal samples were freeze-dried and ®nely ground prior to analysis for DM, GE, nitrogen (N) and titanium dioxide. 2.3. Diets Four experimental diets were evaluated in each trial. All the ingredients were conventional raw materials (Table 1). A feed winter wheat (variety Consort) was Table 1 Diet specification (experimental diets) Ingredient
Inclusion (g/kg)
Trials 1, 2 and 3 Micronized wheat Full fat soya Fish meal Limestone Vitamin-mineral premix (minsal)a Lysine Salt Threonine
700.0 170.0 108.0 3.3 12.5 2.5 2.5 1.2
a Premix (per kg diet): Vitamin A, 12,000 IU; Vitamin D3, 2000 IU; Vitamin E, 50 IU; VitaminB1, 1 mg; Vitamin B2, 3 mg; Vitamin B6, 1 mg; Vitamin B12, 10 mg; Vitamin K, 2 mg; copper (cupric sulphate), 175 mg; nicotinic acid, 12 mg; pantothenic acid, 10 mg; iron, 200 mg; cobalt, 0.5 mg; manganese, 40 mg; zinc, 90 mg, iodine, 1 mg; selenium, 0.2 mg; calcium, 31.25 g; salt, 25 g; sodium, 10 g; provided by Trouw Ltd., Wincham, Northwich, Cheshire, UK.
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obtained and micronized by Dale Country Foods Ltd., Co. Durham, Yorkshire using a Micro Red 20 cereal micronizer with a burner temperature of approximately 2008C, thus, ®nal exit temperatures on leaving the micronizer, based on dwell times, ranged between 85 and 1108C. Flaked cereals were ground through a 5 mm screen and mixed with the basal diet. Diets were manufactured in the University of Nottingham animal feed mill. 2.3.1. Trials 1 and 2 Wheat was micronized at low (dwell time 10 s, LC), standard (dwell time 13 s, SC) and high cook conditions (dwell time 35 s, HC). The objective of Trial 2 was to con®rm the effects obtained from Trial 1 and to examine whether there was an effect of length of time of storage (2 months) of wheat. 2.3.2. Trial 3 The role of steeping/conditioning the grains is that of facilitating heat transfer to the interior of the grain kernel. A 2 2 factorial experiment was designed in order to investigate the effect of two different micronization temperatures and two methods of steeping the grain before being micronized. Wheat grain was steeped for two different lengths of time, 2 (SS) and 12 h (LS). Each batch of the steeped grain was divided into two parts and micronized at two different temperatures: low (dwell time 10 s, LC) and high (dwell time 35 s, HC). 2.4. Chemical analysis of diets and faecal samples All analyses were conducted in duplicate with repetition if variation was >5%. Samples were dried for approximately 48 h in a forced draft oven set at a temperature of 1058C for DM. The N content was determined using a NA 2000 Nitrogen Analyzer (Fisons, UK) and GE, with regular benzoic acid standards, GE with a Parr 1241 adiabatic calorimeter bomb (Parr Instrument Co., Moline, IL, USA). Starch content was estimated by solubilization of starch with dimethyl sulphoxide, sodium acetate buffer and amyloglycosidase enzyme solution. A GOD glucose perid reagent solution (GOD-perid test kit, Boehringer Manhhheim) was used to quantify the released glucose by reading the absorbance with a SP6-500 UV spectrophotometer (Pye Unicam Ltd., Cambridge) at 610 nm. Acid detergent ®bre (ADF) was determined according to the method of Van Soest (1973), but following pre-treatment with a-amylase to dissolve starch more thoroughly. Ether extract (EE) content was determined by extraction with petroleum ether (40±608C) while total fat (prior acid hydrolysis) was evaluated following the method of Sanderson (1986). The procedure of Bedford and Classen (1993), slightly modi®ed by Drakley (personal communication), was followed to measure the in vitro extract viscosity of samples. Minimum and maximum viscosity values are presented as there were dif®culties in obtaining a constant values. TiO2 was determined according to the method of Short et al. (1996). Level of crystallinity was determined by the method of Hermans and Weidinger (1948) as cited by Marsh (1986). The method used was a Siemens 5005 X-ray system modi®ed by the addition of a microcomputer system for the analysis and storage of data. The X-ray
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generator operated at 40 kV and 40 mA. The analysis involves the drawing of a smooth demarcation line on a powder diffractogram, which has been corrected for incoherent scattering, between the background scattering and the crystalline scattering. The ratio of the area enclosed by this line and the diffraction curve above the line to the total area of the diffractogram due to coherent scattering is taken as a measure of the absolute crystallinity. By using an interactive graphics program a smooth curve was drawn between the amorphous and crystalline coherent scattering curves. For ease of interpretation, only the ®rst of the samples (usually the more amorphous one), comes with its actual values, whilst a constant of 200, 400 and 600 was added to the other samples so that visual inspection of treatment differences was facilitated. The ratio of the crystalline area to the total area of the diffractogram gave an estimate of the crystallinity of the sample. The content of gelatinized starch in the cereal samples was calculated: GS R S=R, where GS proportion of gelatinized starch, R degree of crystallinity of the raw sample, S degree of crystallinity of the cooked sample. 2.5. Calculation of results Determination of daily liveweight gain (DLWG) was achieved by linear regression of the weekly liveweight on days, with the slope (which was used in subsequent analysis of variance) being DLWG. This is a more accurate procedure than reliance only on start and end weights and also allows a precise calculation of the number of days that an animal takes to grow over the speci®c weight range of the trials (10±27 kg). Throughout the whole experimental period, total DM fed (feed offered less any refusals) was recorded. Total FI (on DM basis) was divided by the number of days that the animal took to grow over the speci®c live weight range of the experiment giving average daily FI. Food conversion ratio (FCR) was determined on a DM basis. Chemical analyses of diets and faeces allowed calculation of the coef®cient of total tract apparent digestibility (CTTAD) of DM, energy and N. 2.6. Statistical analysis Data were subjected to analysis of variance using the Genstat V program (Lawes agricultural trust, 1984). Trials 1 and 2 were analyzed with time of cooking (being 0 for raw wheat, and 10, 13 and 35 s corresponding to low, standard and high cook temperatures, respectively) as numerical values to establish linear and non-linear contrasts (i.e. regression) rather than as four separate treatments; Trial 3 was analyzed as a 2 time of steeping 2 cooking temperature factorial design. 3. Results 3.1. Trial 1 The chemical composition of wheat is presented in Table 2. As expected DM of micronized wheat was increased with increasing time spent under the micronizer. Starch,
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Fig. 1. Degree of crystallinity for micronized wheat samples (Trial 1).
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Table 2 Trials 1 and 2: chemical analysis of micronized wheata (g/kg DM) DM
Raw wheat Wheat LC Wheat SC Wheat HC a
Starch
N
Total fat
EE
ADF
A
B
A
B
A
B
A
B
A
B
A
B
871 878 888 952
887 894 904 931
676 643 641 674
625 705 685 647
116 115 117 119
121 116 114 117
27 26 26 24
28 24 24 25
17 22 23 18
20 22 20 19
33 20 29 21
43 26 28 23
RW: raw wheat, LC: low cook, SC: standard cook, HC: high cook; A: Trial 1; B: Trial 2.
Table 3 Viscosity (cP) measurements (min±max) and gelatinized starch (proportion of total starch) for micronized wheat Trial 1
Raw Low cook Standard cook High cook
Trial 2
Trial 3
Viscosity
Gelatinized starch
Viscosity
Gelatinized starch
3.10±3.58 4.19±4.68 4.60±4.97 8.15±10.02
0.000 0.086 0.067 0.465
2.34±2.96 4.83±5.67 4.39±5.70 7.74±8.74
0.000 0.093 0.193 0.503
LSLCa LSHCa SSLCa SSHCa
Viscosity
Gelatinized starch
7.00±7.05 7.72±11.80 10.9±13.0 7.05±9.94
0.082 0.592 0.395 0.658
a
LSLC: long steep low cook, LSHC: long steep high cook, SSLC: short steep low cook, SSHC: short steep high cook.
Table 4 Performance and digestibility related measurements obtained with piglets: Trial 1 Diets
Performance a
Coefficient of total tract apparent digestibility a
a
DLWG
FI
FCR
Dry matter
Gross energy Crude protein
Raw wheat Low cook Standard cook High cook
606 548 589 570
810 781 862 837
1.344 1.428 1.466 1.474
0.789 0.820 0.821 0.815
0.797 0.835 0.839 0.828
0.789 0.831 0.816 0.795
S.E.D.c
26.7
27.0
0.0403
0.0239
0.0259
0.0307
P
0.186 0.357 (L)b 0.280 (Q) 0.091 (Dev)
0.036 0.228 (L) 0.640 (Q) 0.008 (Dev)
0.013 0.008 (L) 0.042 (Q) 0.659 (Dev)
0.522 0.423 (L) 0.222 (Q) 0.861(Dev)
0.386 0.407 (L) 0.136 (Q) 0.904 (Dev)
0.526 0.866 (L) 0.189 (Q) 0.548 (Dev)
a
DLWG: daily live weight gain (g per day); FI: feed intake (g DM per day); FCR: feed conversion ratio (g DM per g gain). b Analysis of variance conducted to establish linear (L), non linear (Q) and deviations (Dev) (i.e. higher order polynomial beyond Q) contrasts based on numerical values of 0, 10, 13 and 35 (time of micronizing in seconds), respectively, for raw, low, standard and high cook. c S.E.D.: standard error of difference.
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N, total fat and EE content appeared to remain unchanged with cooking, while ADF was reduced. Cooked samples at lower temperatures showed a higher degree of crystallinity (Fig. 1) while the high cook wheat was substantially non-crystalline. Gelatinized starch and viscosity followed the same trend (Table 3) with values increasing the longer the dwell time (i.e. higher the cooking temperature). The performance and digestibility results from Trial 1 are given in Table 4. No signi®cant differences were observed for DLWG. There were signi®cant effects of cooking temperature on FI (P 0:036), but data appeared to vary in a non-structured fashion (P 0:008 Dev). Feed conversion ratio (FCR) was signi®cantly better for piglets fed diets based on raw wheat (P 0:013; quadratic contrasts, P 0:042, suggest that deterioration in FCR was not apparent after medium cooking times). No signi®cant differences were observed for CTTAD for DM, GE and N. 3.2. Trial 2 The proximate composition (Table 2) and the effects of micronization were similar compared with Trial 1 for total fat and EE. DM of micronized wheat was increased with increasing time spent under the micronizer. Micronization also resulted in a decrease of ADF. Starch content was higher for all micronized samples compared to the raw wheat. Viscosity (Table 3) followed the same pattern as for gelatinized starch; the higher the temperature, the greater the viscosity and the proportion of gelatinized starch (Fig. 2). No signi®cant differences (Table 5) were observed for performance or for CTTAD for DM or GE although differences approached signi®cance for N (P 0:063). Table 5 Performance and digestibility related measurements obtained with piglets: Trial 2 (conducted 2 months after Trial 1)a Wheat diets
Performance b
Coefficient of total tract apparent digestibility b
DLWG
FI
FCR
Raw wheat Low cook Standard cook High cook
543 552 525 567
785 811 770 804
S.E.D.c
31.4
P
0.521 0.295 (L) 0.427 (Q) 0.480 (Dev) a
b
Dry matter
Gross energy
Crude protein
1.457 1.476 1.488 1.437
0.822 0.806 0.820 0.807
0.826 0.810 0.837 0.819
0.838 0.812 0.821 0.789
24.9
0.0683
0.0095
0.0105
0.0161
0.363 0.528 (L) 0.816 (Q) 0.103 (Dev)
0.886 0.666 (L) 0.520 (Q) 0.885 (Dev)
0.282 0.226 (L) 0.735 (Q) 0.137 (Dev)
0.136 0.656 (L) 0.752 (Q) 0.027 (Dev)
0.063 0.012 (L) 0.734 (Q) 0.417 (Dev)
DLWG: daily live weight gain (g per day); FI: feed intake (g DM per day); FCR: feed conversion ratio (g DM per g gain). b Analysis of variance conducted to establish linear (L), non linear (Q) and deviations (Dev) (i.e. higher order polynomial beyond Q) contrasts based on numerical values of 0, 10, 13 and 35 (time of micronizing in seconds), respectively, for raw, low, standard and high cook. c S.E.D.: standard error of difference.
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Fig. 2. Degree of crystallinity for micronized wheat samples (Trial 2).
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Table 6 Chemical analysis of steeped micronized wheata (g/kg DM)
Wheat Wheat Wheat Wheat
LSLC LSHC SSLC SSHC
DM
Starch
N
Total fat
EE
ADF
900 908 895 902
616 646 633 597
118 115 117 115
29 23 26 25
24 21 22 22
14 31 18 23
a LSLC: long steeped low cook, LSHC: long steeped high cook, SSLC: short steeped low cook, SSHC: short steeped high cook.
3.3. Trial 3 Content of DM, N, total fat and EE were not affected to any marked extent, while ADF content was increased with increasing temperature (Table 6). Starch content for LS appeared to be higher in HC than for LC wheat, while the opposite was observed for steeping. Viscosity of the steeped wheat samples (Table 3) followed the same pattern as for the starch content; it was higher with HC for the LS wheat while it was reduced for LS. Gelatinized starch (Table 3) was lower for LSLC (Fig. 3) which showed that wheat cooked at higher temperatures was essentially non-crystalline. Main effects and interaction means for performance and digestibility are presented in Table 7. Signi®cant differences were observed for the effect of steeping the grains prior to micronization for DLWG (P 0:007) and FI (P < 0:001). There was no signi®cant difference observed for FCR. On the other hand, there were no signi®cant differences following the application of two different micronization temperatures for any of the
Fig. 3. Degree of crystallinity for micronized-steeped wheat samples (Trial 3).
LS (12 h)
LSa
SS (2 h)
SSa
LCa
HCa
Low High Low High temperature temperature temperature temperature (LSLC) (LSHC) (SSLC) (SSHC) DLWGb (g per day) Feed intake (g DM per day) FCRb (g DM per g gain) Dry matterd Gross energyd Crude proteind a
475 743 1.579 0.798 0.792 0.799
492 726 1.484 0.827 0.811 0.818
543 789 1.466 0.834 0.833 0.814
529 803 1.529 0.842 0.823 0.823
LS: long steeped; SS: short steeped; LC: low cook; HC: high cook. DLWG: daily live weight gain; FCR: feed conversion ratio. c S.E.D.: standard error of difference. d Coefficient of total tract apparent digestibility. b
484 536 509 510 735 796 766 765 1.531 1.497 1.522 1.506 0.812 0.838 0.816 0.834 0.802 0.828 0.813 0.817 0.808 0.818 0.806 0.820
S.E.D.c S
T
ST
P
P
S.E.D.
P
51.4 23.3 0.0483 0.0110 0.0121 0.0172
0.384 0.356 0.029 0.206 0.129 0.704
36.4 0.007 0.930 16.5 <0.001 0.925 0.0342 0.330 0.646 0.0078 0.006 0.035 0.0086 0.010 0.598 0.0122 0.420 0.278
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Table 7 Main effect means and interaction means with main effect and interactions showing the effect of steeping (S) and temperature (T) on performance and coefficient of total tract apparent digestibility of piglets fed micronized-steeped wheat diets: Trial 3
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parameters investigated; the steeping temperature interaction was not signi®cant for DLWG and FI, but signi®cant for FCR (P 0:029). CTTAD for DM, GE and N followed the same pattern as for performance. Heat treatment was found to be signi®cant for DM (P 0:035). The dominant effect in terms of digestibility was once again the response to different steeping periods. Animals offered the short steeped wheat diets digested signi®cantly more DM (P 0:006) and GE (P 0:010) while N was not affected. 4. Discussion Trials 1 and 2 were conducted with wheat processed under the same conditions and no major differences for gross chemical composition were observed. There were however differences with degree of gelatinzation and in vitro extract viscosity which both tended to increase with higher dwell times during micronization. Trial 3 demonstrated that water and temperature interact when considering these two factors. Native starch granules are insoluble in cold water, but, on heating in suspension, absorb water and swell irreversibly (French, 1984). Loss of order (birefringence) and crystallinity, and the solubilization of amylose accompany swelling. Gelatinization temperatures for wheat range between 60 and 708C (Greenwood, 1970) and heating results in a ¯uid composed of porous, gelatinized and swollen granules with an amylopectin skeleton, suspended in a hot amylose solution. In the current programme, starch remained crystalline under low temperature micronizing, while the gelatinization process was substantially complete at high temperatures. However, a-amylase occasionally cannot effectively penetrate gelatinized starch granules (Wursch et al., 1986) and formation of amyloselipid complexes observed during heat treatment of wheat may retard amylolysis (Holm et al., 1983, 1988). It is possible, therefore, that a reduction in amylolysis may reduce rate passage of digesta, thus, affecting gut ®ll and FI; performance may also be adversely affected. The exact mechanisms by which water is transferred and distributed inside the grain during steeping are not well understood, but it seems that there is a period between 2 and 3 h where it reaches its maximum level; the changes induced by water penetration have been described by Glenn et al. (1991); time and temperature during conditioning may increase the rate of water penetration. Additionally, moisture equilibrium is achieved more rapidly in those grains with a higher initial moisture content (Moss, 1977). Even at low moisture levels, branched structures (trans-glucosidation) formed during heat treatment are not degradable with amylolytic enzymes and represent an irreversible chemical modi®cation (Siljestrom et al., 1986). Therefore, both temperature and moisture content during micronizing may, because of physico-chemical changes resulting, potentially have signi®cant effects on starch structure of wheat, the degree to which it is digested in piglets and their subsequent performance. Results from the current programme indicate that micronization improved potential starch availability (increase in gelatinized starch). However, there were few notable responses observed in the current programme for digestibility. Micronization reduces digestibility of DM, starch and protein (Hristov et al., 1997) although, in certain wheat varieties, starch digestion might be enhanced after being micronized. Huang et al. (1997)
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noticed that micronizing wheat improved the faecal apparent digestibilities in piglets; heat treatment shifted the disappearance of starch from the large to the small intestine, which may result in an improvement in the ef®ciency of energy utilization. It is dif®cult to compare data from the current experiments with the relatively few studies conducted to date with micronized wheat due to different wheat varieties used, initial live weights of the animals and different processing variables involved (which are rarely reported, an exception being Lawrence, 1975). Gill et al. (1996) compared the effect of wheat processing over a 28 day trial period with weaned piglets; in demonstrating a bene®t of extrusion (but not micronizing), a favorable effect of processing on gut health was also observed (reduction in digesta pH of digesta and gut coliform counts. These results agree with those of McCone et al. (1991) where micronized ¯aked wheat depressed DLWG and FCR compared to a pelleted diet containing cold milled wheat which is in agreement with Trial 1. Niu et al. (1996) studied the effect of micronization and tempering (raising the moisture content of the grain) on the nutritional value of wheat for broilers; high temperatures reduced DLWG, but had no effect on FCR. Tempering reduced nutritive value of the wheat, in agreement with the present results (Trial 3). There was good general agreement between Trials 1 and 2 in terms of performance, other than an improvement to digestibility (but deterioration in performance) of diets based on raw wheat, which indicates that storage time over the period of the programme (2 months) was of limited consequence. Whilst micronization results in disruption of the protein matrix surrounding starch granules (Harbers, 1975), thus making it more susceptible to the action of a-amylase, formation of resistant starch during heat processing (Berry, 1986) might be responsible for differences observed during Trial 1 between raw and cooked wheat. Moreover, rupture of branch points in amylopectin during popping of wheat, due to the more extensive starch fragmentation, has been reported to decrease starch hydrolysis (Holm and Bjorck, 1988); however, other than FCR in Trial 1 and N digestibility in Trial 2 (which were both reduced following high temperature micronizing), no major effects on either performance or digestibility were observed during Trials 1 and 2. 5. Conclusions The general conclusions from the current programme are that, with the superiority of raw over micronized wheat (Trial 1) and the lack of any differences obtained in Trial 2, micronization is questionable as an effective means of improving the nutritive value of wheat for weaned piglets. However, short steeping signi®cantly improved DLWG compared with long steeping. It has been demonstrated previously that in vitro or in vivo viscosity of wheat varieties do not necessarily relate to differences in performance (Stewart et al., 1998) which has been con®rmed in the current programme. Although viscosity of micronized steeped wheat samples (Trial 3) correlated with performance data, this was not the case in Trials 1 and 2. Thus, in vitro viscosity values of wheat cannot predict in vivo responses. No correlation between gelatinized starch and performance or digestibility could be made suggesting that, at this live weight and at the rate of wheat employed, production of a-amylase should be adequate. Comparisons between different processing
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technologies have to consider quantifying the variables involved rather than rely simply on the name of a process. Acknowledgements The ®nancial assistance of Greek State Scholarship Foundation (I.K.Y) and co-operation of I'Anson Brothers (Dale county foods Ltd.) for micronizing the wheat is gratefully acknowledged; thanks also to Dr. R. Wulansari at the Division of Food Science at the University of Nottingham, who carried out the X-ray analyses. References Bedford, M.R., Classen, H.L., 1993. An in vitro assay for prediction of broiler intestinal viscosity and growth when fed rye-based diets in the presence of exogenous enzymes. Poult. Sci. 72, 137±143. Berry, C.S., 1986. Resistant starch: formation and measurements of starch that survives exhaustive digestion with amylolytic enzymes during the determination of dietary fibre. J. Cereal Sci. 4, 301±314. Champ, M., Delort-Laval, J., 1991. Effects of processing on chemical characteristics and nutritive value of cereals. Anim. Prod. 52, 564±565 (abstract). French, D., 1984. Organization of starch granules. In: Whilster, R.L., BeMiller, J.B, Paschall, E.F. (Eds.), Starch: Chemistry and Technology. Academic Press, Orlando, USA, pp. 183±247. Gill, B.P., Garcia, S., Hillman, K.H., Schulze, H., 1996. Effect of wheat processing and enzyme supplementation of weaner diets on piglet performance and gut health. J. Anim. Sci. (Pencaitland), 62, 635 (abstract). Glenn, G.M., Younce, F.L., Pitts, M.J., 1991. Fundamental physical properties characterizing the hardness of wheat endosperm. J. Cereal Sci. 13, 179±194. Greenwood, C.T., 1970. Organization of starch granules. In: Pigman, W., Horton, D. (Eds.), The Carbohydrates, Chemistry and Technology, Vol. 2B. 2nd Edition. Academic Press, London, UK, 471 pp. Harbers, L.H., 1975. Starch granules structural changes and amylolytic patterns in processed sorghum grain. J. Anim. Sci. 41, 1496±1501. Holm, J., Bjorck, I., 1988. Effects of thermal processing of wheat on starch: II. Enzymic availability. J. Cereal Sci. 8, 261±268. Holm, J., Bjorck, I., Ostrowska, S., Eliasson, A.-C., Asp, N.-G., Larsson, K., Lundquist, I., 1983. Digestibility of amylose-lipid complexes in vitro. Digestibility of amylose-lipid complexes in vitro and in vivo. Starch/Starke 35, 294±297. Holm, J., Bjorck, I., Eliasson, A.-C., 1988. Effects of thermal processing of wheat on starch: I. Physico-chemical and functional properties. J. Cereal Sci. 8, 249±260. Hoover, R., Vasanthan, T., 1994. Effect of heat-moisture treatment on the structure and physicochemical properties of cereal, legume and tuber starches. Carbohydrate Res. 252, 33±53. Hristov, A., McAllister, T.A., Xu, Z., Dong, Y., Pickard, M.D., Cheng, K.-J., 1997. The effect of variety and micronization on the situ digestion of wheat. Can. J. Anim. Sci. 77, 548±549. Huang, S.X., Sauer, W.C., Hargreaves, L., Pickard, M., Li, S., 1997. Effect of micronization on energy, starch and amino acid digestibilities in wheat for young pigs. J. Anim. Feed Sci. 6, 353±368. Lawes Agricultural Trust, 1984. Genstat V, Release 3, Statistics Department, Rothamstead Experimental Station. Lawrence, T.L.J., 1973a. An evaluation of the micronization process for preparing cereals for the growing pig: 1. Effects on digestibility and nitrogen retention. Anim. Prod. 16, 99±107. Lawrence, T.L.J., 1973b. An evaluation of the micronization process for preparing cereals for the growing pig: 2. Effects on growth rate, food conversion efficiency and carcass characteristics. Anim. Prod. 16, 109±116. Lawrence, T.L.J., 1975. An evaluation of the micronization process for preparing cereals for the growing pig: 3. A note on the effect of micronization temperature on the nutritive value of wheat. Anim. Prod. 20, 167±170.
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Marsh, R.D.L., 1986. A study of the retrogradation of wheat starch systems using X-ray diffraction. Ph.D. thesis, University of Nottingham, UK. McCone, S., English, P.R., Fowler, V.R., Gill, B.P., Birnie, M., Davidson, F.M., 1991. The effects of cereal flaking and diet pelleting on the voluntary intake and performance of weaned piglets. Anim. Prod. 52, 600 (abstract). Moss, R., 1977. The influence of endosperm structure, protein content and grain moisture on the rate of water penetration into wheat during conditioning. J. Food Technpol. 12, 275±283. Niu, Z.Y., Classen, H.L., Bennett, C.D., 1996. The effect of micronization, tempering and enzyme addition on the feeding value of wheat for broiler chickens. Poult. Sci. 75 (Suppl. 1), 15. Sanderson, P., 1986. A new method of analysis of feedingstuffs for the determination of crude oils and fats, In: Haresign, W., Cole, D.J.A. (Eds.), Recent Advances in Animal Nutrition, Butterworths, London, pp. 77±81. Short, F.J., Gorton, P., Wiseman, J., Boorman, K.N., 1996. Determination of titanium dioxide added as an inert marker in chicken digestibility studies. Anim. Feed Sci. Technol. 59, 215±221. Siljestrom, M., Westerlund, E., Bjorck, I., Holm, J., Asp, N.-G., Theander, O., 1986. The effect of various thermal processes on dietary fibre and starch content of whole grain wheat and white flour. J. Cereal Sci. 4, 315±323. Stewart, R.A., McAllister, A., McRacken, K.J., 1998. Effects of thermal wheat source, heat treatment and enzyme inclusion on diet metabolizability and broiler performance. Br. Poult. Sci. 39 (Suppl. 1), S42. Van Soest, P.J., 1973. Collaborative study of acid detergent fibre and lignin. J. Assoc. Offic. Anal. Chem. 56, 781±784. Wursch, P., Del Vedovo, S., Koellrevtter, B., 1986. Cell structure and starch nature as a key determinants of the digestion rate of starch in legume. Am. J. Clin. Nutr. 43, 25±29.
In¯uence of processing variables during micronization of wheat on starch structure and subsequent performance and digestibility in weaned piglets fed wheat-based diets L.N. Zarkadas1, J. Wiseman* Division of Agriculture and Horticulture, School of BioSciences, University of Nottingham, Sutton Bonington Campus, Loughborough, Leics, LE12 5RD, UK Received 21 February 2000; received in revised form 13 March 2001; accepted 29 March 2001
Abstract Physical and nutritional characteristics of wheat following micronization were determined in three experiments, each based on four treatments with four gilts and four entire males (from 10 to 27 kg liveweight) per treatment all using the same batch of wheat, designed to investigate the effect of temperatures (different heating time, Trials 1 and 2) and preconditioning (steeping the grains for different lengths of time) prior to different micronization temperatures (Trial 3). Micronization of wheat reduced crystallinity, as detected through X-ray diffractogram analysis, and increased gelatinized starch and viscosity in vitro particularly when preconditioned. Coef®cients of total tract apparent digestibilities (CTTAD) of dry matter (DM), gross energy (GE) and nitrogen (N) of diets containing wheat were not signi®cantly different between treatments (Trial 1) neither was daily liveweight gain (DLWG). Diets containing raw wheat had signi®cantly better (P 0:013) feed conversion ratio (FCR). Similar responses were obtained in Trial 2 suggesting limited effect of storage time prior to micronization. The in¯uence of preconditioning (2 and 12 h steeping time) followed by low and high cook conditions was examined in Trial 3. Signi®cant improvements for the shorter versus longer steeping time for DLWG (536 versus 484 g per day, P 0:007), feed intake (FI, 796 versus 735 g DM per day, P < 0:001), CTTAD for DM (0.838 versus 0.812, P 0:006) and GE (0.828 versus 0.802, P 0:010) were observed, while interaction of steeping time temperature was signi®cant for FCR (P 0:029). No effect of heating time was observed. There were no correlations between animal responses within individual trials and wheat starch crystallinity or viscosity (in vitro assessments). In conclusion, the addition of wheat micronized
* Corresponding author. Tel.: 44-115-9516054; fax: 44-115-9516060. E-mail address: [email protected] (J. Wiseman). 1 Co-corresponding author.
0377-8401/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 7 - 8 4 0 1 ( 0 1 ) 0 0 2 6 6 - 8
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under different conditions did not improve piglet performance although pre-conditioning did have an effect. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Micronization; Wheat; Starch; Gelatinization; Piglet; Digestibility; Performance
1. Introduction Processing applied to feedstuffs is both expensive and time-consuming and would not be undertaken unless it offered advantages, both biological and economic. Cold/hot, dry/wet, mechanical and chemical methods of treatment may be used, with the objectives of improving palatability (promoting feed intake (FI)), avoiding wastage and enhancing performance. Other objectives would be to improve digestibility and/or nutritive value (Champ and Delort-Laval, 1991), to prevent spoilage and inactivate heat labile antinutritional factors. Heat treatment of cereals alters kernel structure, thus, enhancing release of starch granules from the protein matrix and disrupting their order during gelatinization (i.e. degree of crystallinity) resulting in increased susceptibility to enzyme activity (Hoover and Vasanthan, 1994) which should increase carbohydrate utilization. Micronization is a short time high temperature cooking process using moisture, temperature and mechanical pressure to achieve conditions for optimum cooking and starch gelatinization (Lawrence, 1973a). Grains are preconditioned to increase moisture content and are heated on a vibrating bed under a radiant heat source (gas heaters, which emit energy principally in the infrared region of the electromagnetic spectrum) for a speci®c time depending on the product and then ¯aked. Performance of growing ®nishing pigs has been shown to be improved following micronization of cereals (Lawrence, 1973a) associated with increased digestibility of diet dry matter (DM), gross energy (GE) (Lawrence, 1973b) and amino acids (Huang et al., 1997). Many studies have evaluated the effects of processing which, however, tend to be limited to a consideration of a named process only. There are a number of variables associated with each process whose nutritional consequences have not been widely studied making conclusions on the effect of processing dif®cult to draw. The objective of the current programme was to investigate the effect of different micronization temperatures of wheat as well as the effect of pre-conditioning the grain prior to heat treatment at known temperatures on physico-chemical characteristics and on performance and digestibility when included in diets for weaned piglets (10±27 kg). 2. Experimental 2.1. Animals, housing and management All three experiments were conducted similarly based on the same batch of wheat. A total of 32 piglets (16 of each sex) from the University of Nottingham herd (commercial white hybrid) weaned between 24 and 25 days of age (8±10 kg) were employed for each
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trial. Animals were individually weighed, transferred to an environmentally controlled room (experimental unit), housed in individual pens with semi slatted ¯oors, two nipple drinkers and a feed trough. A commercial weaner diet was offered twice daily, at 08.30 and 17.00 h during the acclimatization period (6±7 days) at the end of which piglets were weighed and randomly allocated to one of four experimental diets which were offered on a restricted basis, 0.95 of assumed ad libitum intake, in relation to live weight. At feeding, diets were mixed in the approximate proportions water:food 2:1 to avoid dust and spillage. Water was also available ad libitum. Any feed wasted was removed, dried, weighed and a sample retained for DM determination. Liveweight and FI were determined weekly and the trial concluded when animals reached 27 kg liveweight. 2.2. Digestibility study Digestibility of each experimental diet was determined using four pigs per diet once a pig had reached a liveweight of 15 kg. Each meal allowance during the digestibility study contained the inert marker titanium dioxide (TiO2) at a rate of 1 g/kg diet and was fed for 5 days. Following that, the grills on the ¯oor of each cage were cleaned thoroughly following the morning feed and diets were fed for an additional 5 days during a collection period during which, on each day, a fresh faecal sample was removed from each pen at regular intervals during the day (animals were checked every 2 h) and stored in a plastic bag, for each pig, at 208C immediately after each collection. The grills of each ¯oor were cleaned daily after the morning feed. Faecal samples were freeze-dried and ®nely ground prior to analysis for DM, GE, nitrogen (N) and titanium dioxide. 2.3. Diets Four experimental diets were evaluated in each trial. All the ingredients were conventional raw materials (Table 1). A feed winter wheat (variety Consort) was Table 1 Diet specification (experimental diets) Ingredient
Inclusion (g/kg)
Trials 1, 2 and 3 Micronized wheat Full fat soya Fish meal Limestone Vitamin-mineral premix (minsal)a Lysine Salt Threonine
700.0 170.0 108.0 3.3 12.5 2.5 2.5 1.2
a Premix (per kg diet): Vitamin A, 12,000 IU; Vitamin D3, 2000 IU; Vitamin E, 50 IU; VitaminB1, 1 mg; Vitamin B2, 3 mg; Vitamin B6, 1 mg; Vitamin B12, 10 mg; Vitamin K, 2 mg; copper (cupric sulphate), 175 mg; nicotinic acid, 12 mg; pantothenic acid, 10 mg; iron, 200 mg; cobalt, 0.5 mg; manganese, 40 mg; zinc, 90 mg, iodine, 1 mg; selenium, 0.2 mg; calcium, 31.25 g; salt, 25 g; sodium, 10 g; provided by Trouw Ltd., Wincham, Northwich, Cheshire, UK.
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obtained and micronized by Dale Country Foods Ltd., Co. Durham, Yorkshire using a Micro Red 20 cereal micronizer with a burner temperature of approximately 2008C, thus, ®nal exit temperatures on leaving the micronizer, based on dwell times, ranged between 85 and 1108C. Flaked cereals were ground through a 5 mm screen and mixed with the basal diet. Diets were manufactured in the University of Nottingham animal feed mill. 2.3.1. Trials 1 and 2 Wheat was micronized at low (dwell time 10 s, LC), standard (dwell time 13 s, SC) and high cook conditions (dwell time 35 s, HC). The objective of Trial 2 was to con®rm the effects obtained from Trial 1 and to examine whether there was an effect of length of time of storage (2 months) of wheat. 2.3.2. Trial 3 The role of steeping/conditioning the grains is that of facilitating heat transfer to the interior of the grain kernel. A 2 2 factorial experiment was designed in order to investigate the effect of two different micronization temperatures and two methods of steeping the grain before being micronized. Wheat grain was steeped for two different lengths of time, 2 (SS) and 12 h (LS). Each batch of the steeped grain was divided into two parts and micronized at two different temperatures: low (dwell time 10 s, LC) and high (dwell time 35 s, HC). 2.4. Chemical analysis of diets and faecal samples All analyses were conducted in duplicate with repetition if variation was >5%. Samples were dried for approximately 48 h in a forced draft oven set at a temperature of 1058C for DM. The N content was determined using a NA 2000 Nitrogen Analyzer (Fisons, UK) and GE, with regular benzoic acid standards, GE with a Parr 1241 adiabatic calorimeter bomb (Parr Instrument Co., Moline, IL, USA). Starch content was estimated by solubilization of starch with dimethyl sulphoxide, sodium acetate buffer and amyloglycosidase enzyme solution. A GOD glucose perid reagent solution (GOD-perid test kit, Boehringer Manhhheim) was used to quantify the released glucose by reading the absorbance with a SP6-500 UV spectrophotometer (Pye Unicam Ltd., Cambridge) at 610 nm. Acid detergent ®bre (ADF) was determined according to the method of Van Soest (1973), but following pre-treatment with a-amylase to dissolve starch more thoroughly. Ether extract (EE) content was determined by extraction with petroleum ether (40±608C) while total fat (prior acid hydrolysis) was evaluated following the method of Sanderson (1986). The procedure of Bedford and Classen (1993), slightly modi®ed by Drakley (personal communication), was followed to measure the in vitro extract viscosity of samples. Minimum and maximum viscosity values are presented as there were dif®culties in obtaining a constant values. TiO2 was determined according to the method of Short et al. (1996). Level of crystallinity was determined by the method of Hermans and Weidinger (1948) as cited by Marsh (1986). The method used was a Siemens 5005 X-ray system modi®ed by the addition of a microcomputer system for the analysis and storage of data. The X-ray
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generator operated at 40 kV and 40 mA. The analysis involves the drawing of a smooth demarcation line on a powder diffractogram, which has been corrected for incoherent scattering, between the background scattering and the crystalline scattering. The ratio of the area enclosed by this line and the diffraction curve above the line to the total area of the diffractogram due to coherent scattering is taken as a measure of the absolute crystallinity. By using an interactive graphics program a smooth curve was drawn between the amorphous and crystalline coherent scattering curves. For ease of interpretation, only the ®rst of the samples (usually the more amorphous one), comes with its actual values, whilst a constant of 200, 400 and 600 was added to the other samples so that visual inspection of treatment differences was facilitated. The ratio of the crystalline area to the total area of the diffractogram gave an estimate of the crystallinity of the sample. The content of gelatinized starch in the cereal samples was calculated: GS R S=R, where GS proportion of gelatinized starch, R degree of crystallinity of the raw sample, S degree of crystallinity of the cooked sample. 2.5. Calculation of results Determination of daily liveweight gain (DLWG) was achieved by linear regression of the weekly liveweight on days, with the slope (which was used in subsequent analysis of variance) being DLWG. This is a more accurate procedure than reliance only on start and end weights and also allows a precise calculation of the number of days that an animal takes to grow over the speci®c weight range of the trials (10±27 kg). Throughout the whole experimental period, total DM fed (feed offered less any refusals) was recorded. Total FI (on DM basis) was divided by the number of days that the animal took to grow over the speci®c live weight range of the experiment giving average daily FI. Food conversion ratio (FCR) was determined on a DM basis. Chemical analyses of diets and faeces allowed calculation of the coef®cient of total tract apparent digestibility (CTTAD) of DM, energy and N. 2.6. Statistical analysis Data were subjected to analysis of variance using the Genstat V program (Lawes agricultural trust, 1984). Trials 1 and 2 were analyzed with time of cooking (being 0 for raw wheat, and 10, 13 and 35 s corresponding to low, standard and high cook temperatures, respectively) as numerical values to establish linear and non-linear contrasts (i.e. regression) rather than as four separate treatments; Trial 3 was analyzed as a 2 time of steeping 2 cooking temperature factorial design. 3. Results 3.1. Trial 1 The chemical composition of wheat is presented in Table 2. As expected DM of micronized wheat was increased with increasing time spent under the micronizer. Starch,
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Fig. 1. Degree of crystallinity for micronized wheat samples (Trial 1).
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Table 2 Trials 1 and 2: chemical analysis of micronized wheata (g/kg DM) DM
Raw wheat Wheat LC Wheat SC Wheat HC a
Starch
N
Total fat
EE
ADF
A
B
A
B
A
B
A
B
A
B
A
B
871 878 888 952
887 894 904 931
676 643 641 674
625 705 685 647
116 115 117 119
121 116 114 117
27 26 26 24
28 24 24 25
17 22 23 18
20 22 20 19
33 20 29 21
43 26 28 23
RW: raw wheat, LC: low cook, SC: standard cook, HC: high cook; A: Trial 1; B: Trial 2.
Table 3 Viscosity (cP) measurements (min±max) and gelatinized starch (proportion of total starch) for micronized wheat Trial 1
Raw Low cook Standard cook High cook
Trial 2
Trial 3
Viscosity
Gelatinized starch
Viscosity
Gelatinized starch
3.10±3.58 4.19±4.68 4.60±4.97 8.15±10.02
0.000 0.086 0.067 0.465
2.34±2.96 4.83±5.67 4.39±5.70 7.74±8.74
0.000 0.093 0.193 0.503
LSLCa LSHCa SSLCa SSHCa
Viscosity
Gelatinized starch
7.00±7.05 7.72±11.80 10.9±13.0 7.05±9.94
0.082 0.592 0.395 0.658
a
LSLC: long steep low cook, LSHC: long steep high cook, SSLC: short steep low cook, SSHC: short steep high cook.
Table 4 Performance and digestibility related measurements obtained with piglets: Trial 1 Diets
Performance a
Coefficient of total tract apparent digestibility a
a
DLWG
FI
FCR
Dry matter
Gross energy Crude protein
Raw wheat Low cook Standard cook High cook
606 548 589 570
810 781 862 837
1.344 1.428 1.466 1.474
0.789 0.820 0.821 0.815
0.797 0.835 0.839 0.828
0.789 0.831 0.816 0.795
S.E.D.c
26.7
27.0
0.0403
0.0239
0.0259
0.0307
P
0.186 0.357 (L)b 0.280 (Q) 0.091 (Dev)
0.036 0.228 (L) 0.640 (Q) 0.008 (Dev)
0.013 0.008 (L) 0.042 (Q) 0.659 (Dev)
0.522 0.423 (L) 0.222 (Q) 0.861(Dev)
0.386 0.407 (L) 0.136 (Q) 0.904 (Dev)
0.526 0.866 (L) 0.189 (Q) 0.548 (Dev)
a
DLWG: daily live weight gain (g per day); FI: feed intake (g DM per day); FCR: feed conversion ratio (g DM per g gain). b Analysis of variance conducted to establish linear (L), non linear (Q) and deviations (Dev) (i.e. higher order polynomial beyond Q) contrasts based on numerical values of 0, 10, 13 and 35 (time of micronizing in seconds), respectively, for raw, low, standard and high cook. c S.E.D.: standard error of difference.
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N, total fat and EE content appeared to remain unchanged with cooking, while ADF was reduced. Cooked samples at lower temperatures showed a higher degree of crystallinity (Fig. 1) while the high cook wheat was substantially non-crystalline. Gelatinized starch and viscosity followed the same trend (Table 3) with values increasing the longer the dwell time (i.e. higher the cooking temperature). The performance and digestibility results from Trial 1 are given in Table 4. No signi®cant differences were observed for DLWG. There were signi®cant effects of cooking temperature on FI (P 0:036), but data appeared to vary in a non-structured fashion (P 0:008 Dev). Feed conversion ratio (FCR) was signi®cantly better for piglets fed diets based on raw wheat (P 0:013; quadratic contrasts, P 0:042, suggest that deterioration in FCR was not apparent after medium cooking times). No signi®cant differences were observed for CTTAD for DM, GE and N. 3.2. Trial 2 The proximate composition (Table 2) and the effects of micronization were similar compared with Trial 1 for total fat and EE. DM of micronized wheat was increased with increasing time spent under the micronizer. Micronization also resulted in a decrease of ADF. Starch content was higher for all micronized samples compared to the raw wheat. Viscosity (Table 3) followed the same pattern as for gelatinized starch; the higher the temperature, the greater the viscosity and the proportion of gelatinized starch (Fig. 2). No signi®cant differences (Table 5) were observed for performance or for CTTAD for DM or GE although differences approached signi®cance for N (P 0:063). Table 5 Performance and digestibility related measurements obtained with piglets: Trial 2 (conducted 2 months after Trial 1)a Wheat diets
Performance b
Coefficient of total tract apparent digestibility b
DLWG
FI
FCR
Raw wheat Low cook Standard cook High cook
543 552 525 567
785 811 770 804
S.E.D.c
31.4
P
0.521 0.295 (L) 0.427 (Q) 0.480 (Dev) a
b
Dry matter
Gross energy
Crude protein
1.457 1.476 1.488 1.437
0.822 0.806 0.820 0.807
0.826 0.810 0.837 0.819
0.838 0.812 0.821 0.789
24.9
0.0683
0.0095
0.0105
0.0161
0.363 0.528 (L) 0.816 (Q) 0.103 (Dev)
0.886 0.666 (L) 0.520 (Q) 0.885 (Dev)
0.282 0.226 (L) 0.735 (Q) 0.137 (Dev)
0.136 0.656 (L) 0.752 (Q) 0.027 (Dev)
0.063 0.012 (L) 0.734 (Q) 0.417 (Dev)
DLWG: daily live weight gain (g per day); FI: feed intake (g DM per day); FCR: feed conversion ratio (g DM per g gain). b Analysis of variance conducted to establish linear (L), non linear (Q) and deviations (Dev) (i.e. higher order polynomial beyond Q) contrasts based on numerical values of 0, 10, 13 and 35 (time of micronizing in seconds), respectively, for raw, low, standard and high cook. c S.E.D.: standard error of difference.
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Fig. 2. Degree of crystallinity for micronized wheat samples (Trial 2).
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Table 6 Chemical analysis of steeped micronized wheata (g/kg DM)
Wheat Wheat Wheat Wheat
LSLC LSHC SSLC SSHC
DM
Starch
N
Total fat
EE
ADF
900 908 895 902
616 646 633 597
118 115 117 115
29 23 26 25
24 21 22 22
14 31 18 23
a LSLC: long steeped low cook, LSHC: long steeped high cook, SSLC: short steeped low cook, SSHC: short steeped high cook.
3.3. Trial 3 Content of DM, N, total fat and EE were not affected to any marked extent, while ADF content was increased with increasing temperature (Table 6). Starch content for LS appeared to be higher in HC than for LC wheat, while the opposite was observed for steeping. Viscosity of the steeped wheat samples (Table 3) followed the same pattern as for the starch content; it was higher with HC for the LS wheat while it was reduced for LS. Gelatinized starch (Table 3) was lower for LSLC (Fig. 3) which showed that wheat cooked at higher temperatures was essentially non-crystalline. Main effects and interaction means for performance and digestibility are presented in Table 7. Signi®cant differences were observed for the effect of steeping the grains prior to micronization for DLWG (P 0:007) and FI (P < 0:001). There was no signi®cant difference observed for FCR. On the other hand, there were no signi®cant differences following the application of two different micronization temperatures for any of the
Fig. 3. Degree of crystallinity for micronized-steeped wheat samples (Trial 3).
LS (12 h)
LSa
SS (2 h)
SSa
LCa
HCa
Low High Low High temperature temperature temperature temperature (LSLC) (LSHC) (SSLC) (SSHC) DLWGb (g per day) Feed intake (g DM per day) FCRb (g DM per g gain) Dry matterd Gross energyd Crude proteind a
475 743 1.579 0.798 0.792 0.799
492 726 1.484 0.827 0.811 0.818
543 789 1.466 0.834 0.833 0.814
529 803 1.529 0.842 0.823 0.823
LS: long steeped; SS: short steeped; LC: low cook; HC: high cook. DLWG: daily live weight gain; FCR: feed conversion ratio. c S.E.D.: standard error of difference. d Coefficient of total tract apparent digestibility. b
484 536 509 510 735 796 766 765 1.531 1.497 1.522 1.506 0.812 0.838 0.816 0.834 0.802 0.828 0.813 0.817 0.808 0.818 0.806 0.820
S.E.D.c S
T
ST
P
P
S.E.D.
P
51.4 23.3 0.0483 0.0110 0.0121 0.0172
0.384 0.356 0.029 0.206 0.129 0.704
36.4 0.007 0.930 16.5 <0.001 0.925 0.0342 0.330 0.646 0.0078 0.006 0.035 0.0086 0.010 0.598 0.0122 0.420 0.278
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Table 7 Main effect means and interaction means with main effect and interactions showing the effect of steeping (S) and temperature (T) on performance and coefficient of total tract apparent digestibility of piglets fed micronized-steeped wheat diets: Trial 3
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parameters investigated; the steeping temperature interaction was not signi®cant for DLWG and FI, but signi®cant for FCR (P 0:029). CTTAD for DM, GE and N followed the same pattern as for performance. Heat treatment was found to be signi®cant for DM (P 0:035). The dominant effect in terms of digestibility was once again the response to different steeping periods. Animals offered the short steeped wheat diets digested signi®cantly more DM (P 0:006) and GE (P 0:010) while N was not affected. 4. Discussion Trials 1 and 2 were conducted with wheat processed under the same conditions and no major differences for gross chemical composition were observed. There were however differences with degree of gelatinzation and in vitro extract viscosity which both tended to increase with higher dwell times during micronization. Trial 3 demonstrated that water and temperature interact when considering these two factors. Native starch granules are insoluble in cold water, but, on heating in suspension, absorb water and swell irreversibly (French, 1984). Loss of order (birefringence) and crystallinity, and the solubilization of amylose accompany swelling. Gelatinization temperatures for wheat range between 60 and 708C (Greenwood, 1970) and heating results in a ¯uid composed of porous, gelatinized and swollen granules with an amylopectin skeleton, suspended in a hot amylose solution. In the current programme, starch remained crystalline under low temperature micronizing, while the gelatinization process was substantially complete at high temperatures. However, a-amylase occasionally cannot effectively penetrate gelatinized starch granules (Wursch et al., 1986) and formation of amyloselipid complexes observed during heat treatment of wheat may retard amylolysis (Holm et al., 1983, 1988). It is possible, therefore, that a reduction in amylolysis may reduce rate passage of digesta, thus, affecting gut ®ll and FI; performance may also be adversely affected. The exact mechanisms by which water is transferred and distributed inside the grain during steeping are not well understood, but it seems that there is a period between 2 and 3 h where it reaches its maximum level; the changes induced by water penetration have been described by Glenn et al. (1991); time and temperature during conditioning may increase the rate of water penetration. Additionally, moisture equilibrium is achieved more rapidly in those grains with a higher initial moisture content (Moss, 1977). Even at low moisture levels, branched structures (trans-glucosidation) formed during heat treatment are not degradable with amylolytic enzymes and represent an irreversible chemical modi®cation (Siljestrom et al., 1986). Therefore, both temperature and moisture content during micronizing may, because of physico-chemical changes resulting, potentially have signi®cant effects on starch structure of wheat, the degree to which it is digested in piglets and their subsequent performance. Results from the current programme indicate that micronization improved potential starch availability (increase in gelatinized starch). However, there were few notable responses observed in the current programme for digestibility. Micronization reduces digestibility of DM, starch and protein (Hristov et al., 1997) although, in certain wheat varieties, starch digestion might be enhanced after being micronized. Huang et al. (1997)
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noticed that micronizing wheat improved the faecal apparent digestibilities in piglets; heat treatment shifted the disappearance of starch from the large to the small intestine, which may result in an improvement in the ef®ciency of energy utilization. It is dif®cult to compare data from the current experiments with the relatively few studies conducted to date with micronized wheat due to different wheat varieties used, initial live weights of the animals and different processing variables involved (which are rarely reported, an exception being Lawrence, 1975). Gill et al. (1996) compared the effect of wheat processing over a 28 day trial period with weaned piglets; in demonstrating a bene®t of extrusion (but not micronizing), a favorable effect of processing on gut health was also observed (reduction in digesta pH of digesta and gut coliform counts. These results agree with those of McCone et al. (1991) where micronized ¯aked wheat depressed DLWG and FCR compared to a pelleted diet containing cold milled wheat which is in agreement with Trial 1. Niu et al. (1996) studied the effect of micronization and tempering (raising the moisture content of the grain) on the nutritional value of wheat for broilers; high temperatures reduced DLWG, but had no effect on FCR. Tempering reduced nutritive value of the wheat, in agreement with the present results (Trial 3). There was good general agreement between Trials 1 and 2 in terms of performance, other than an improvement to digestibility (but deterioration in performance) of diets based on raw wheat, which indicates that storage time over the period of the programme (2 months) was of limited consequence. Whilst micronization results in disruption of the protein matrix surrounding starch granules (Harbers, 1975), thus making it more susceptible to the action of a-amylase, formation of resistant starch during heat processing (Berry, 1986) might be responsible for differences observed during Trial 1 between raw and cooked wheat. Moreover, rupture of branch points in amylopectin during popping of wheat, due to the more extensive starch fragmentation, has been reported to decrease starch hydrolysis (Holm and Bjorck, 1988); however, other than FCR in Trial 1 and N digestibility in Trial 2 (which were both reduced following high temperature micronizing), no major effects on either performance or digestibility were observed during Trials 1 and 2. 5. Conclusions The general conclusions from the current programme are that, with the superiority of raw over micronized wheat (Trial 1) and the lack of any differences obtained in Trial 2, micronization is questionable as an effective means of improving the nutritive value of wheat for weaned piglets. However, short steeping signi®cantly improved DLWG compared with long steeping. It has been demonstrated previously that in vitro or in vivo viscosity of wheat varieties do not necessarily relate to differences in performance (Stewart et al., 1998) which has been con®rmed in the current programme. Although viscosity of micronized steeped wheat samples (Trial 3) correlated with performance data, this was not the case in Trials 1 and 2. Thus, in vitro viscosity values of wheat cannot predict in vivo responses. No correlation between gelatinized starch and performance or digestibility could be made suggesting that, at this live weight and at the rate of wheat employed, production of a-amylase should be adequate. Comparisons between different processing
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technologies have to consider quantifying the variables involved rather than rely simply on the name of a process. Acknowledgements The ®nancial assistance of Greek State Scholarship Foundation (I.K.Y) and co-operation of I'Anson Brothers (Dale county foods Ltd.) for micronizing the wheat is gratefully acknowledged; thanks also to Dr. R. Wulansari at the Division of Food Science at the University of Nottingham, who carried out the X-ray analyses. References Bedford, M.R., Classen, H.L., 1993. An in vitro assay for prediction of broiler intestinal viscosity and growth when fed rye-based diets in the presence of exogenous enzymes. Poult. Sci. 72, 137±143. Berry, C.S., 1986. Resistant starch: formation and measurements of starch that survives exhaustive digestion with amylolytic enzymes during the determination of dietary fibre. J. Cereal Sci. 4, 301±314. Champ, M., Delort-Laval, J., 1991. Effects of processing on chemical characteristics and nutritive value of cereals. Anim. Prod. 52, 564±565 (abstract). French, D., 1984. Organization of starch granules. In: Whilster, R.L., BeMiller, J.B, Paschall, E.F. (Eds.), Starch: Chemistry and Technology. Academic Press, Orlando, USA, pp. 183±247. Gill, B.P., Garcia, S., Hillman, K.H., Schulze, H., 1996. Effect of wheat processing and enzyme supplementation of weaner diets on piglet performance and gut health. J. Anim. Sci. (Pencaitland), 62, 635 (abstract). Glenn, G.M., Younce, F.L., Pitts, M.J., 1991. Fundamental physical properties characterizing the hardness of wheat endosperm. J. Cereal Sci. 13, 179±194. Greenwood, C.T., 1970. Organization of starch granules. In: Pigman, W., Horton, D. (Eds.), The Carbohydrates, Chemistry and Technology, Vol. 2B. 2nd Edition. Academic Press, London, UK, 471 pp. Harbers, L.H., 1975. Starch granules structural changes and amylolytic patterns in processed sorghum grain. J. Anim. Sci. 41, 1496±1501. Holm, J., Bjorck, I., 1988. Effects of thermal processing of wheat on starch: II. Enzymic availability. J. Cereal Sci. 8, 261±268. Holm, J., Bjorck, I., Ostrowska, S., Eliasson, A.-C., Asp, N.-G., Larsson, K., Lundquist, I., 1983. Digestibility of amylose-lipid complexes in vitro. Digestibility of amylose-lipid complexes in vitro and in vivo. Starch/Starke 35, 294±297. Holm, J., Bjorck, I., Eliasson, A.-C., 1988. Effects of thermal processing of wheat on starch: I. Physico-chemical and functional properties. J. Cereal Sci. 8, 249±260. Hoover, R., Vasanthan, T., 1994. Effect of heat-moisture treatment on the structure and physicochemical properties of cereal, legume and tuber starches. Carbohydrate Res. 252, 33±53. Hristov, A., McAllister, T.A., Xu, Z., Dong, Y., Pickard, M.D., Cheng, K.-J., 1997. The effect of variety and micronization on the situ digestion of wheat. Can. J. Anim. Sci. 77, 548±549. Huang, S.X., Sauer, W.C., Hargreaves, L., Pickard, M., Li, S., 1997. Effect of micronization on energy, starch and amino acid digestibilities in wheat for young pigs. J. Anim. Feed Sci. 6, 353±368. Lawes Agricultural Trust, 1984. Genstat V, Release 3, Statistics Department, Rothamstead Experimental Station. Lawrence, T.L.J., 1973a. An evaluation of the micronization process for preparing cereals for the growing pig: 1. Effects on digestibility and nitrogen retention. Anim. Prod. 16, 99±107. Lawrence, T.L.J., 1973b. An evaluation of the micronization process for preparing cereals for the growing pig: 2. Effects on growth rate, food conversion efficiency and carcass characteristics. Anim. Prod. 16, 109±116. Lawrence, T.L.J., 1975. An evaluation of the micronization process for preparing cereals for the growing pig: 3. A note on the effect of micronization temperature on the nutritive value of wheat. Anim. Prod. 20, 167±170.
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