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Chemical composition and physical properties of modified dietary fibre sources
Food Hydrocolloids val.l no.1 pp.57-64, 1986
Chemical composition and physical properties of modified dietary fibre sources Eva Arrigoni, Andrea Caprez, Renato Amado! and Hans Neukom
Swiss Federal Institute of Technology, Department of Food Science, ETHZentrum, CH-8092 Zurich. Switzerland iTo whom reprint requests should be sent Abstract. The influence of thermal treatments on the chemical composition and the physical properties of yellow pea hulls, apple pomace and depectinised apple pomace were determined. The chemical composition of yellow pea hulls and apple pomace was altered only slightly. With depectinised apple pomace, however, the heat treatments led to a significant loss of the total dietary fibre (TDF) content. Water uptake, water binding capacity, rheological behaviour in the farinograph and oil absorption were determined before and after boiling, autoclaving and extrusion cooking. The physical properties of all samples were considerably affected by the thermal modifications. Whilst in cooked dietary fibre samples the water uptake, the water binding capacity and the oil absorption was always enhanced, the influence of autoclaving and extrusion cooking on the physical properties depended very much on the dietary fibre source. Yellow pea hulls showed unchanged or slightly increased values, while the results for the two apple pomace preparations were lower compared with the untreated samples. The differences in the farinograms-were less obvious since the dietary fibre content in the dough mixtures was only in the range of 10-20%.
Introduction Different sources of dietary fibre have been added to food material. Among these, wheat bran is the most important. It has been applied mainly for fibre enrichment in cereal products (1). The lightly coloured yellow pea hulls have also been used and shown to be suitable for incorporation into different bread types (2,3). Apple pomace, which exhibits a very pleasant fruity taste, is obtained during juice preparation or pectin production and has been added to bread and pastry (4) as well as used for supplementation of farinaceous products (5) (e.g. pasta). Little information is available on the effects of the added dietary fibre on the final products. Food processing usually involves some sort of heat treatment by which the added dietary fibre material may be affected. In a previous study (6) it was demonstrated that different thermal modifications of wheat bran affected primarily the physical properties of this dietary fibre source, whereas the chemical composition was only slightly changed. The purpose of the present work was to investigate the effects of different thermal treatments on both the chemical composition and the physical properties of yellow pea hulls and apple pomace. Materials and methods Yellow pea hulls, dried apple pomace and dried, depectinised apple pomace were obtained from local manufacturers (Knorr-Nahrmittel AG, Thayngen, and Obipektin AG, BischofszeII, Switzerland).
© IRL Press Limited, Oxford, England
57
E.Arrigoni et aI.
Modifications The folIowing modifications of the dietary fibre sources were carried out.
Boiling . 15,30 or 60 min in a 10-fold amount of water at 100°C (11 ofwater/IOO g of sample). Autoclaving. 15,30 or 60 min in an autoclave at 121°C at a pres sure of2 bars without addition of water . Extrusion . Extrusion cooking on a single-screw Buss Kneading-Extruder (Buss AG, Pratteln, Switzerland) by using the following process conditions for yellow pea hulls and depectinised apple pomace: screw temperature 100 and 200 °C, barrel temperature 100 and 200°C , screw speed 100 and 160 r.p.m., mass feed rate 9.9 and 10.3 kg/h. Slip-on clements of varying screw geometry were used to increase the mechanical energy. Before the extrusion process , the yellow pea hulIs were moistened to a water content of 20% . The depectinised apple pomace was used directly (30% dry matter) for extrusion and had to be dried subsequently in vacuum at 0 .03-0.04 bar, 70°C. The boiled and autoclaved samples were freeze-dried after cooling to a moisture content of 2 -8.5 %. All modifications of yellow pea hulls and apple pomace were carried out with coarse material, whereas depectinised apple pomace was milled (Condux Universal Mill, Wolfgang/Hanau , FRG, feed rate 150-200 kg/h) to a particle size of 0 .4 mm before boiling and autoclaving.
Sample preparation Prior to the different analyses modified samples with a particle size above 0 .5 mm were milled in a Cyclotec mill (Tecator AB, Hoganas, Sweden) ; alI others were used directly.
Chemical analyses The determination of dietary fibre and the analyses of the chemical composition of the dietary fibre sources as well as of the modified materials were performed by methods described by Arrigoni et al. (7) . Dietary fibre content was determined after enzymatic degradation of starch and protein by gravimetric measurement. Starch was degraded by the action of Termamyl [NovoFerment (Schweiz) AG, Basel, Switzerland] and subsequent fungal glucoamylase (BDH Chemicals Ltd, Poole, UK) treatment. The proteins were removed by degradation with Protease P-5380 from Bacillus subtilis (Sigma Chemicals, St Louis, MO, USA). The insoluble dietary fibre (IDF) was weighed after centrifugation, washing of the residue and drying at 105°C. The supernatant of the centrifugation was dialysed against distilled water and freeze-dried to yield the soluble dietary fibre (SDF) fraction (7) . The pectin content of the two apple pomace samples was determined before and after the modification procedures by the method described by Blumenkrantz and AsboeHansen (8), which is based on a colour reaction between uronic acid and m-hydroxydiphenyl. 58
Effects of thermal treatments on dietary fibre sources
Moisture contents were determined by drying at 105°C to constant weight, protein contents were calculated as the sum of amino acids after protein hydrolysis and amino acid analysis. Lipids were determined after acid treatment and extraction of the total lipid fraction with light petroleum. Ash contents were measured after mineralisation in a muffle furnace at 600°C for 10 h.
Physical analyses The methods used for the determination of water uptake, water binding capacity and rheological behaviour as measured in the farinograph and the oil absorption have been described by Caprez et al. (6). The determination of water uptake was carried out by a method developed by Enslin (9), adapted to the requirements of dietary fibre at our laboratory. The water binding capacity was measured by the official AACC-method (10) for proteinaceous material, modified to the special requirements for dietary fibres. The soaking time of the samples in water was extended to 24 h and the decanting step was replaced by aspirating the supernatant very carefully after centrifugation. From the farinograms, the maximum resistance, mixing time and mixing tolerance index were calculated for a flour-water mixture. The reference sample, a patent flour, was adjusted with 187 ml of water to 500 Brabender units,at the maximum resistance. The same amount of water was used for the dietary fibre - flour mixtures. For yellow pea hulls and depectinised apple pomace, mixtures of 80% patent flour and 20% dietary fibre material were used. This concentration of dietary fibre material in doughs is common for enriched pastry and breads. For the rheological measurements of apple pomace, only 10% of the flour could be replaced to remain in a comparable range.
Statistical evaluations All analyses were performed at least in duplicate and the means obtained were compared with the untreated samples (control). The statistical calculations were done by Student's t test. Table 1. Chemical composition of yellow pea hulls. apple pomace and depectinised apple pomace (% dry matter). Yellow pea hulls
Apple pomace
Depectinised Apple pomace
Insoluble (IDF) Soluble (SDF) Total (TDF)
85.3 5.3 90.6
55.5 10.5 65.9
78.0 14.0 92.0
Protein" in TDF (%) Total protein" Pectin Lipids Ash
1.0 5.8 ND 0.6 2.4
4.2 4.4 17.8 2.3 1.7
5.3 6.6 14.1 4.1 2.7
Components Dietary fibre
ND: not determined. "Protein content is calculated as sum of amino acids.
59
E.Arrigoni et aJ.
Results and Discussion Chemical analyses The chemical composition of the starting materials is shown in Table 1. A comparison of the results with other published data is not possible, since only crude fibre or neutral detergent fibre values for yellow pea hulls and apple pomace are ava ilable (2,11,12). In addition , the composition of the dietary fibre sources varies in rather broad ranges depending on their provenance (variety, production methods, etc. ). To our knowledge, results concerning depectinised apple pomace are presented for the first time in this report. It should be noted that only a relatively small amount of pectin is removed from the pomace during industrial depectination. The pectin content, expressed as uronic acid, decreases from 17.8 to 14.1 %. Compared with wheat bran, yellow pea hulls and depectinised apple pomace samples show a much higher content of total dietary fibre, mainly due to the large amount of insoluble fibre material present in these fibre sources. During pectin extraction some of the soluble fibre material, arabans, arabinogalactans and galactans, which are associated with the pectic substances, are degraded by the acid conditions used. The content of dietary fibre in the modified samples is given in Table II. A wet heat Table II. Dietary fibre components of yellow pea hulls. apple pomace and depectin ised apple pomace after modification (% dry matter) . % protein' in TDF
Dietary fibre Insoluble (IDF)
Soluble (SDF)
Total (TDF)
85.3 82.9 85.3 81.7 80 .8 81.1
5.3 9.8 9.0 9 .7 12.5 6.7
90.6 92.7 94.3 b 91.3 93.3h 87.8 b
1.0 1.6 1.7 1.1 1.8 1.4
55.5 48 .5 45 .9 50 .2 43 .7
10.5 12.0 18.4 18.0 19.2
65.9 6O.5 b 64.3 68.2 b 62.9
4 .2 4.9 b 5.5 b
78.0 72.0 72.3 69.7 82.0
14.0 10.9 10.7 11.0 8.9
92.0 82.8 b 83.0 b 80.7 b 90.9
5.3 5.1 5.5 5.5 4.5 b
Yellow pea hulls Untreated Boiled 60 min Autoclavcd 15 min Autoclaved 30 min Autoclaved 60 min Extruded Apple pomace Untreated Boiled 15 min Boiled 60 min Autoclaved 30 min Autoclaved 60 min
6.l b 5.0b
Depectinised apple pomace Untreated Boiled 15 min Autoclavcd 15 min Autoclaved 60 min Extruded
'Protein content is calculated as sum of amino acids. bSignificantly different (P < 0.05) from control (untreated) samples.
60
Effects of thermal treatments on dietary fibre sources
treatment of yellow pea hulls leads to an increase in total dietary fibre (TDF). In addition, a shift from IDF to SDF occurs, indicating a partial solubilisation of dietary fibre material without degradation of the macromolecular structures. The mechanical stress during extrusion cooking results in a loss ofIDF, thus yielding an overall decrease in dietary fibre material. The insoluble fibre content of all modified apple pomace samples is lower than in untreated samples, whereas the SDF content is higher. The longer the heat treatment lasts , the larger the shift toward soluble fibres. The increase in SDF material is probably due to solubilisation of pectic substances and associated hemicelluloses. Anderson and Clydesdale (13) have demonstrated this behaviour of pectin during wet treatment. These findings were also confirmed by Schwerdtfeger and Hentschel (14) , who clearly showed a solubilisation of pectic substances during boiling. The residual protein content after all types of thermal modifications is significantly increased . As shown for wheat bran (6), enzymatically resistant protein-dietary fibre complexes are formed during the modification procedures. In depectinised apple pomace, wet thermal treatment reduces both the IDF and SDF content. The solubilisation and the degradation of the dietary fibre material, especially araban, is obviously favoured by the low pH value of the samples (pH 1.8-2.0). Residual hydrochloric acid from the pectin extraction procedure induces partial acid hydrolysis of the dietary fibre during wet heat treatment. Extrusion cooking of depectinised apple pomace also leads to a loss of SDF material, probably due to the same reasons.
Physical properties Figure I shows the water uptake of the untreated and modified fibre preparations. The water uptake, measured by the Enslin method, is increased for all dietary fibre sources investigated after boiling . This type of heat treatment changes considerably the structure of the fibre material, thus allowing an increased water uptake . Non-depectinised modified apple pomace samples show a slower water uptake during the early stages of the determination. The wetability of the material is lowered compared with the untreated sample . Even after 60 min the water uptake is not completed. This can be deduced from the curve still being steep at the end of the determination. The same observations could be made with apple pomace after autoclaving. In this case, however, the final values are lower than for the untreated sample. Yellow pea hulls and depectinised apple pomace also showed lower final values for the autoclaved samples compared with the untreated ones. Extrusion cooking leads to the same changes in water uptake as boiling. The results of the investigations on the water binding capacity, the parameters obtained from the farinograms as well as the values for the oil absorption of the untreated and the thermally modified fibre samples are summarised in Table III. Wet heat treatment gives a distinct increase in the water binding capacity of yellow pea hulls. For the apple pomace samples, only the non-depectinised material is able to bind considerably more water than the untreated reference rnaterial . After extrusion cooking the water binding capacity for the yellow pea hulls remains unchanged, whereas the values for the depec tinised apple pomace sample increases. Doughs , consisting of mixtures of patent flour (80 and 90% respectively) and untreated as well as modified dietary fibre material (20% yellow pea hulls and depcctinised apple pomace, and 10% apple pomace), were prepared in order to establish the 61
E.Arrigoni et al.
influence of the latter on the different physical dough properties. For yellow pea hulls, only high temperatures lead to a change of the kneading parameters (increase of the dough resistance). Depectinised apple pomace which had undergone only mild thermal treatment shows little change in rheological behaviour of the dough. A considerable decrease of the dough resistance is observed when apple pomace , which was autoclav ed for 60 min, was added to the flour. Above all , the boiled (15 min) and autoclaved (30 min) apple pomace supplementation, increased maximal dough resistance, so that only 10% of these materials can be replaced in the flour-dietary fibre mixture. Apple YELLOW PEA HULLS BOl LED
- -- - _. -
400
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-
-
-
-
YELLOW PEA HULL5 AUTOCL AVEO
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-
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-
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-
- -
I I
zoo 100
100
o
10
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40
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APP LE Pc.
7. HZO
YELLOW PE A HULL5 E XTRUDED
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/'
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(
400
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I
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;( Hz O 500
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OEPE CTINI SED APPLE POMACE BOlLED
HZO
o
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20
30
40
50
60
MIN
Effects or thermal treatments on dietary fibre sources OEPE CTI N ISEO APPLE POMACE EXTRUDE D
DE P ECTI NIS EO APP LE PO MACE AUTOCL AVEO 40 0
300
300
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200
10 0
10 0
o
10
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.- - - - - - - - - -
D
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MIN
Fig. 1. Water uptake of modified dietary fibre material and compar ison with untreated sample . - Untreated ; . .. . . . . 15 min heat treatme nt; - - - - 30 min heat treatment ; - - - 60 min heat treatment ; - ' extruded . Table III. Physical propert ies of yellow pea hulls. apple pomace and depectinised apple pomace after modificat ion. Water bind ing capacit y
Farinogram"
Oil absorption
(gIg OM)
mr (BU)
mt (min)
mti (BU)
3.3 5.0 4 .0 3.7 3.7 3.3
800 800 760 910 860 790
9.0 10.0 10.3 12.0 10.0 13.5
30 40 10 70 70 60
0.9 b 0 .9 b NO
5. 1 6.2 6.2 4.5 4.2
740 880 740 950 770
11.0 13.0 29.0 14.5 9.0
170 170 70 220 ISO
1.9 2 .9 b 3.5 b 1.3b 0.9b
2.3 2.5 2.1 2.0 3.0
750 740 750
25 .0 43.0 26.0 22.0 25.0
10 40 80 40
1.4 2 .8b
90
NO
(gIg OM)
Yellow pea hulls Untreated Boiled 60 min Autoclaved 15 min Autoclaved 30 min Autoclaved 60 min Extruded
1.0 1.0 1.1
Apple poma ce" Untreated Boiled 15 min Boiled 60 min Autoclaved 30 min Autocla ved 60 min Depectini sed appl e pomac e Untreated Boiled IS min Autoclav ed 15 min Autoclav ed 60 min Extruded
660
790
1.2 1.3
OM : dry matte r; NO : not determ ined; mr: maximum resistance ; mt: mixing time ; mti: mixing tolerance index; BU: Brabender units. "Only 10% apple pomace for the farinograph. bSignificantiy different (P < 0.05 ) from control (untreated) samples .
pomace, which was boiled for 60 min, prolongs the mixing time considerably, thus indicating a low wetability. The same tendency had been demonstrated with the water uptake exper iments.
63
E.Arrigoni et al.
The ability of the untreated and modified dietary fibre samples to absorb oil is dependent on the surface of the particles. An increase in oil absorption could only be demonstrated for the cooked apple pomace samples. It is not clear if the pectic substances present in the apple pomace have an influence on the changes obtained with these materials. Thermal modifications of yellow pea hulls and apple pomace have little or no influence on the chemical composition of these dietary fibre source. The results obtained in the present investigation confirm the observations made with wheat bran (6). Depectinised apple pomace showed to be an exception, in that heat treatment significantly lowers the TDF content. For this fibre source, the low pH of the sample may play a determinant role as mentioned above. The physical properties of all samples have been considerably affected by the thermal treatment. Although the TDF content does not alter much during thermal modifications, the changes in the physical properties of thedifferent samples seem to be related to single components within the fibre material. It is not known which components are responsible for these effects. This again correlates with the results obtained with wheat bran (6). It is obvious from our experiments that results obtained with one dietary fibre source should not be transferred to another. Exact measurements of the physical properties are very important for technological purposes. However, the physiological effect of thermally treated dietary fibre should not be affected, since the water binding capacity remains high. Acknowledgements
The authors thank the companies Biihler AG (Uzwil, Switzerland) and Buss AG (Pratteln, Switzerland) for permission to use their facilities. The skilful technical assistance of Mr A.Schiippi and the financial support from the Swiss Commission for the Promotion of Scientific Research (project no. 1172) is gratefully acknowledged. References
i.senei.w. (1979) Gordian, 79, 297-300. 2. Satin,M., McKeown,B. and Findlay,C. (1978) Cereal Foods World, 23, 676 -680. 3. Morris,C.E. (1981) Food Eng., 53, 69. 4. Morris,C.E. (1985) Food Eng., 57, 72. 5. Nolan,A.L. (1983) Food Eng., 55,63. 6. Caprez,A., Arrigoni,E.. Arnado.R. and Neukom,H. (1986) J. Cereal Sci., in press. 7. Arrigoni,E., Caprez,A., Arnado.R. and Neukom,H. (1984) Z. Lebensm. Unters. Forsch., 178, 195-198. 8. Blumenkrantz,N. and Asboe-Hansen.G. (1973) Anal. Biochem., 54, 484-489. 9. Enslin.O, (1933) Chem. Fabrik, 6, 147-148. 10. American Association of Cereal Chemists (1978) Method 88-04. 11. Mahalko,J.R., Sandstead,H.H., Johnson,L.K., Inman,L.F., Milne.D.B., Warner,R.C. and Haunz.E.A. (1984) Am. J. Clin. Nutr., 39, 25-34. 12. Waugh,AJ.B. (1981) S. Afr. Food Rev., 8, 27. 13. Anderson,N.E. and Clydesdale,F.M. (1980) J. Food Sci., 45, 1533-1537. 14. Schwerdtfeger,E. and Hentschel,H. (1985) Ernahrungs-Umschau, 32, 145-148.
64
Chemical composition and physical properties of modified dietary fibre sources Eva Arrigoni, Andrea Caprez, Renato Amado! and Hans Neukom
Swiss Federal Institute of Technology, Department of Food Science, ETHZentrum, CH-8092 Zurich. Switzerland iTo whom reprint requests should be sent Abstract. The influence of thermal treatments on the chemical composition and the physical properties of yellow pea hulls, apple pomace and depectinised apple pomace were determined. The chemical composition of yellow pea hulls and apple pomace was altered only slightly. With depectinised apple pomace, however, the heat treatments led to a significant loss of the total dietary fibre (TDF) content. Water uptake, water binding capacity, rheological behaviour in the farinograph and oil absorption were determined before and after boiling, autoclaving and extrusion cooking. The physical properties of all samples were considerably affected by the thermal modifications. Whilst in cooked dietary fibre samples the water uptake, the water binding capacity and the oil absorption was always enhanced, the influence of autoclaving and extrusion cooking on the physical properties depended very much on the dietary fibre source. Yellow pea hulls showed unchanged or slightly increased values, while the results for the two apple pomace preparations were lower compared with the untreated samples. The differences in the farinograms-were less obvious since the dietary fibre content in the dough mixtures was only in the range of 10-20%.
Introduction Different sources of dietary fibre have been added to food material. Among these, wheat bran is the most important. It has been applied mainly for fibre enrichment in cereal products (1). The lightly coloured yellow pea hulls have also been used and shown to be suitable for incorporation into different bread types (2,3). Apple pomace, which exhibits a very pleasant fruity taste, is obtained during juice preparation or pectin production and has been added to bread and pastry (4) as well as used for supplementation of farinaceous products (5) (e.g. pasta). Little information is available on the effects of the added dietary fibre on the final products. Food processing usually involves some sort of heat treatment by which the added dietary fibre material may be affected. In a previous study (6) it was demonstrated that different thermal modifications of wheat bran affected primarily the physical properties of this dietary fibre source, whereas the chemical composition was only slightly changed. The purpose of the present work was to investigate the effects of different thermal treatments on both the chemical composition and the physical properties of yellow pea hulls and apple pomace. Materials and methods Yellow pea hulls, dried apple pomace and dried, depectinised apple pomace were obtained from local manufacturers (Knorr-Nahrmittel AG, Thayngen, and Obipektin AG, BischofszeII, Switzerland).
© IRL Press Limited, Oxford, England
57
E.Arrigoni et aI.
Modifications The folIowing modifications of the dietary fibre sources were carried out.
Boiling . 15,30 or 60 min in a 10-fold amount of water at 100°C (11 ofwater/IOO g of sample). Autoclaving. 15,30 or 60 min in an autoclave at 121°C at a pres sure of2 bars without addition of water . Extrusion . Extrusion cooking on a single-screw Buss Kneading-Extruder (Buss AG, Pratteln, Switzerland) by using the following process conditions for yellow pea hulls and depectinised apple pomace: screw temperature 100 and 200 °C, barrel temperature 100 and 200°C , screw speed 100 and 160 r.p.m., mass feed rate 9.9 and 10.3 kg/h. Slip-on clements of varying screw geometry were used to increase the mechanical energy. Before the extrusion process , the yellow pea hulIs were moistened to a water content of 20% . The depectinised apple pomace was used directly (30% dry matter) for extrusion and had to be dried subsequently in vacuum at 0 .03-0.04 bar, 70°C. The boiled and autoclaved samples were freeze-dried after cooling to a moisture content of 2 -8.5 %. All modifications of yellow pea hulls and apple pomace were carried out with coarse material, whereas depectinised apple pomace was milled (Condux Universal Mill, Wolfgang/Hanau , FRG, feed rate 150-200 kg/h) to a particle size of 0 .4 mm before boiling and autoclaving.
Sample preparation Prior to the different analyses modified samples with a particle size above 0 .5 mm were milled in a Cyclotec mill (Tecator AB, Hoganas, Sweden) ; alI others were used directly.
Chemical analyses The determination of dietary fibre and the analyses of the chemical composition of the dietary fibre sources as well as of the modified materials were performed by methods described by Arrigoni et al. (7) . Dietary fibre content was determined after enzymatic degradation of starch and protein by gravimetric measurement. Starch was degraded by the action of Termamyl [NovoFerment (Schweiz) AG, Basel, Switzerland] and subsequent fungal glucoamylase (BDH Chemicals Ltd, Poole, UK) treatment. The proteins were removed by degradation with Protease P-5380 from Bacillus subtilis (Sigma Chemicals, St Louis, MO, USA). The insoluble dietary fibre (IDF) was weighed after centrifugation, washing of the residue and drying at 105°C. The supernatant of the centrifugation was dialysed against distilled water and freeze-dried to yield the soluble dietary fibre (SDF) fraction (7) . The pectin content of the two apple pomace samples was determined before and after the modification procedures by the method described by Blumenkrantz and AsboeHansen (8), which is based on a colour reaction between uronic acid and m-hydroxydiphenyl. 58
Effects of thermal treatments on dietary fibre sources
Moisture contents were determined by drying at 105°C to constant weight, protein contents were calculated as the sum of amino acids after protein hydrolysis and amino acid analysis. Lipids were determined after acid treatment and extraction of the total lipid fraction with light petroleum. Ash contents were measured after mineralisation in a muffle furnace at 600°C for 10 h.
Physical analyses The methods used for the determination of water uptake, water binding capacity and rheological behaviour as measured in the farinograph and the oil absorption have been described by Caprez et al. (6). The determination of water uptake was carried out by a method developed by Enslin (9), adapted to the requirements of dietary fibre at our laboratory. The water binding capacity was measured by the official AACC-method (10) for proteinaceous material, modified to the special requirements for dietary fibres. The soaking time of the samples in water was extended to 24 h and the decanting step was replaced by aspirating the supernatant very carefully after centrifugation. From the farinograms, the maximum resistance, mixing time and mixing tolerance index were calculated for a flour-water mixture. The reference sample, a patent flour, was adjusted with 187 ml of water to 500 Brabender units,at the maximum resistance. The same amount of water was used for the dietary fibre - flour mixtures. For yellow pea hulls and depectinised apple pomace, mixtures of 80% patent flour and 20% dietary fibre material were used. This concentration of dietary fibre material in doughs is common for enriched pastry and breads. For the rheological measurements of apple pomace, only 10% of the flour could be replaced to remain in a comparable range.
Statistical evaluations All analyses were performed at least in duplicate and the means obtained were compared with the untreated samples (control). The statistical calculations were done by Student's t test. Table 1. Chemical composition of yellow pea hulls. apple pomace and depectinised apple pomace (% dry matter). Yellow pea hulls
Apple pomace
Depectinised Apple pomace
Insoluble (IDF) Soluble (SDF) Total (TDF)
85.3 5.3 90.6
55.5 10.5 65.9
78.0 14.0 92.0
Protein" in TDF (%) Total protein" Pectin Lipids Ash
1.0 5.8 ND 0.6 2.4
4.2 4.4 17.8 2.3 1.7
5.3 6.6 14.1 4.1 2.7
Components Dietary fibre
ND: not determined. "Protein content is calculated as sum of amino acids.
59
E.Arrigoni et aJ.
Results and Discussion Chemical analyses The chemical composition of the starting materials is shown in Table 1. A comparison of the results with other published data is not possible, since only crude fibre or neutral detergent fibre values for yellow pea hulls and apple pomace are ava ilable (2,11,12). In addition , the composition of the dietary fibre sources varies in rather broad ranges depending on their provenance (variety, production methods, etc. ). To our knowledge, results concerning depectinised apple pomace are presented for the first time in this report. It should be noted that only a relatively small amount of pectin is removed from the pomace during industrial depectination. The pectin content, expressed as uronic acid, decreases from 17.8 to 14.1 %. Compared with wheat bran, yellow pea hulls and depectinised apple pomace samples show a much higher content of total dietary fibre, mainly due to the large amount of insoluble fibre material present in these fibre sources. During pectin extraction some of the soluble fibre material, arabans, arabinogalactans and galactans, which are associated with the pectic substances, are degraded by the acid conditions used. The content of dietary fibre in the modified samples is given in Table II. A wet heat Table II. Dietary fibre components of yellow pea hulls. apple pomace and depectin ised apple pomace after modification (% dry matter) . % protein' in TDF
Dietary fibre Insoluble (IDF)
Soluble (SDF)
Total (TDF)
85.3 82.9 85.3 81.7 80 .8 81.1
5.3 9.8 9.0 9 .7 12.5 6.7
90.6 92.7 94.3 b 91.3 93.3h 87.8 b
1.0 1.6 1.7 1.1 1.8 1.4
55.5 48 .5 45 .9 50 .2 43 .7
10.5 12.0 18.4 18.0 19.2
65.9 6O.5 b 64.3 68.2 b 62.9
4 .2 4.9 b 5.5 b
78.0 72.0 72.3 69.7 82.0
14.0 10.9 10.7 11.0 8.9
92.0 82.8 b 83.0 b 80.7 b 90.9
5.3 5.1 5.5 5.5 4.5 b
Yellow pea hulls Untreated Boiled 60 min Autoclavcd 15 min Autoclaved 30 min Autoclaved 60 min Extruded Apple pomace Untreated Boiled 15 min Boiled 60 min Autoclaved 30 min Autoclaved 60 min
6.l b 5.0b
Depectinised apple pomace Untreated Boiled 15 min Autoclavcd 15 min Autoclaved 60 min Extruded
'Protein content is calculated as sum of amino acids. bSignificantly different (P < 0.05) from control (untreated) samples.
60
Effects of thermal treatments on dietary fibre sources
treatment of yellow pea hulls leads to an increase in total dietary fibre (TDF). In addition, a shift from IDF to SDF occurs, indicating a partial solubilisation of dietary fibre material without degradation of the macromolecular structures. The mechanical stress during extrusion cooking results in a loss ofIDF, thus yielding an overall decrease in dietary fibre material. The insoluble fibre content of all modified apple pomace samples is lower than in untreated samples, whereas the SDF content is higher. The longer the heat treatment lasts , the larger the shift toward soluble fibres. The increase in SDF material is probably due to solubilisation of pectic substances and associated hemicelluloses. Anderson and Clydesdale (13) have demonstrated this behaviour of pectin during wet treatment. These findings were also confirmed by Schwerdtfeger and Hentschel (14) , who clearly showed a solubilisation of pectic substances during boiling. The residual protein content after all types of thermal modifications is significantly increased . As shown for wheat bran (6), enzymatically resistant protein-dietary fibre complexes are formed during the modification procedures. In depectinised apple pomace, wet thermal treatment reduces both the IDF and SDF content. The solubilisation and the degradation of the dietary fibre material, especially araban, is obviously favoured by the low pH value of the samples (pH 1.8-2.0). Residual hydrochloric acid from the pectin extraction procedure induces partial acid hydrolysis of the dietary fibre during wet heat treatment. Extrusion cooking of depectinised apple pomace also leads to a loss of SDF material, probably due to the same reasons.
Physical properties Figure I shows the water uptake of the untreated and modified fibre preparations. The water uptake, measured by the Enslin method, is increased for all dietary fibre sources investigated after boiling . This type of heat treatment changes considerably the structure of the fibre material, thus allowing an increased water uptake . Non-depectinised modified apple pomace samples show a slower water uptake during the early stages of the determination. The wetability of the material is lowered compared with the untreated sample . Even after 60 min the water uptake is not completed. This can be deduced from the curve still being steep at the end of the determination. The same observations could be made with apple pomace after autoclaving. In this case, however, the final values are lower than for the untreated sample. Yellow pea hulls and depectinised apple pomace also showed lower final values for the autoclaved samples compared with the untreated ones. Extrusion cooking leads to the same changes in water uptake as boiling. The results of the investigations on the water binding capacity, the parameters obtained from the farinograms as well as the values for the oil absorption of the untreated and the thermally modified fibre samples are summarised in Table III. Wet heat treatment gives a distinct increase in the water binding capacity of yellow pea hulls. For the apple pomace samples, only the non-depectinised material is able to bind considerably more water than the untreated reference rnaterial . After extrusion cooking the water binding capacity for the yellow pea hulls remains unchanged, whereas the values for the depec tinised apple pomace sample increases. Doughs , consisting of mixtures of patent flour (80 and 90% respectively) and untreated as well as modified dietary fibre material (20% yellow pea hulls and depcctinised apple pomace, and 10% apple pomace), were prepared in order to establish the 61
E.Arrigoni et al.
influence of the latter on the different physical dough properties. For yellow pea hulls, only high temperatures lead to a change of the kneading parameters (increase of the dough resistance). Depectinised apple pomace which had undergone only mild thermal treatment shows little change in rheological behaviour of the dough. A considerable decrease of the dough resistance is observed when apple pomace , which was autoclav ed for 60 min, was added to the flour. Above all , the boiled (15 min) and autoclaved (30 min) apple pomace supplementation, increased maximal dough resistance, so that only 10% of these materials can be replaced in the flour-dietary fibre mixture. Apple YELLOW PEA HULLS BOl LED
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Effects or thermal treatments on dietary fibre sources OEPE CTI N ISEO APPLE POMACE EXTRUDE D
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Fig. 1. Water uptake of modified dietary fibre material and compar ison with untreated sample . - Untreated ; . .. . . . . 15 min heat treatme nt; - - - - 30 min heat treatment ; - - - 60 min heat treatment ; - ' extruded . Table III. Physical propert ies of yellow pea hulls. apple pomace and depectinised apple pomace after modificat ion. Water bind ing capacit y
Farinogram"
Oil absorption
(gIg OM)
mr (BU)
mt (min)
mti (BU)
3.3 5.0 4 .0 3.7 3.7 3.3
800 800 760 910 860 790
9.0 10.0 10.3 12.0 10.0 13.5
30 40 10 70 70 60
0.9 b 0 .9 b NO
5. 1 6.2 6.2 4.5 4.2
740 880 740 950 770
11.0 13.0 29.0 14.5 9.0
170 170 70 220 ISO
1.9 2 .9 b 3.5 b 1.3b 0.9b
2.3 2.5 2.1 2.0 3.0
750 740 750
25 .0 43.0 26.0 22.0 25.0
10 40 80 40
1.4 2 .8b
90
NO
(gIg OM)
Yellow pea hulls Untreated Boiled 60 min Autoclaved 15 min Autoclaved 30 min Autoclaved 60 min Extruded
1.0 1.0 1.1
Apple poma ce" Untreated Boiled 15 min Boiled 60 min Autoclaved 30 min Autocla ved 60 min Depectini sed appl e pomac e Untreated Boiled IS min Autoclav ed 15 min Autoclav ed 60 min Extruded
660
790
1.2 1.3
OM : dry matte r; NO : not determ ined; mr: maximum resistance ; mt: mixing time ; mti: mixing tolerance index; BU: Brabender units. "Only 10% apple pomace for the farinograph. bSignificantiy different (P < 0.05 ) from control (untreated) samples .
pomace, which was boiled for 60 min, prolongs the mixing time considerably, thus indicating a low wetability. The same tendency had been demonstrated with the water uptake exper iments.
63
E.Arrigoni et al.
The ability of the untreated and modified dietary fibre samples to absorb oil is dependent on the surface of the particles. An increase in oil absorption could only be demonstrated for the cooked apple pomace samples. It is not clear if the pectic substances present in the apple pomace have an influence on the changes obtained with these materials. Thermal modifications of yellow pea hulls and apple pomace have little or no influence on the chemical composition of these dietary fibre source. The results obtained in the present investigation confirm the observations made with wheat bran (6). Depectinised apple pomace showed to be an exception, in that heat treatment significantly lowers the TDF content. For this fibre source, the low pH of the sample may play a determinant role as mentioned above. The physical properties of all samples have been considerably affected by the thermal treatment. Although the TDF content does not alter much during thermal modifications, the changes in the physical properties of thedifferent samples seem to be related to single components within the fibre material. It is not known which components are responsible for these effects. This again correlates with the results obtained with wheat bran (6). It is obvious from our experiments that results obtained with one dietary fibre source should not be transferred to another. Exact measurements of the physical properties are very important for technological purposes. However, the physiological effect of thermally treated dietary fibre should not be affected, since the water binding capacity remains high. Acknowledgements
The authors thank the companies Biihler AG (Uzwil, Switzerland) and Buss AG (Pratteln, Switzerland) for permission to use their facilities. The skilful technical assistance of Mr A.Schiippi and the financial support from the Swiss Commission for the Promotion of Scientific Research (project no. 1172) is gratefully acknowledged. References
i.senei.w. (1979) Gordian, 79, 297-300. 2. Satin,M., McKeown,B. and Findlay,C. (1978) Cereal Foods World, 23, 676 -680. 3. Morris,C.E. (1981) Food Eng., 53, 69. 4. Morris,C.E. (1985) Food Eng., 57, 72. 5. Nolan,A.L. (1983) Food Eng., 55,63. 6. Caprez,A., Arrigoni,E.. Arnado.R. and Neukom,H. (1986) J. Cereal Sci., in press. 7. Arrigoni,E., Caprez,A., Arnado.R. and Neukom,H. (1984) Z. Lebensm. Unters. Forsch., 178, 195-198. 8. Blumenkrantz,N. and Asboe-Hansen.G. (1973) Anal. Biochem., 54, 484-489. 9. Enslin.O, (1933) Chem. Fabrik, 6, 147-148. 10. American Association of Cereal Chemists (1978) Method 88-04. 11. Mahalko,J.R., Sandstead,H.H., Johnson,L.K., Inman,L.F., Milne.D.B., Warner,R.C. and Haunz.E.A. (1984) Am. J. Clin. Nutr., 39, 25-34. 12. Waugh,AJ.B. (1981) S. Afr. Food Rev., 8, 27. 13. Anderson,N.E. and Clydesdale,F.M. (1980) J. Food Sci., 45, 1533-1537. 14. Schwerdtfeger,E. and Hentschel,H. (1985) Ernahrungs-Umschau, 32, 145-148.
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