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Effects of extrusion temperature and feed composition on the functional, physical and sensory properties of chestnut and rice flour-based snack-like products
Food Research International 37 (2004) 527–534 www.elsevier.com/locate/foodres
Effects of extrusion temperature and feed composition on the functional, physical and sensory properties of chestnut and rice flour-based snack-like products G. Sacchetti b
a,*
, G.G. Pinnavaia b, E. Guidolin c, M. Dalla Rosa
d
a Dipartimento di Scienze degli Alimenti, Universita degli Studi di Teramo, Via Spagna 1, Mosciano Stazione, 64023 Teramo, Italy Dipartimento di Protezione e Valorizzazione Agro-Alimentare, Universita degli Studi di Bologna, Sede di Cesena, Via Ravennate 1020, 47023 Cesena, Italy c MAFIN S.p.a. Strada degli Alberi, 7, 35015 Galliera Veneta (PD), Italy d Dipartimento di Scienze degli Alimenti, Universita degli Studi di Bologna, Sede di Cesena, Via Ravennate 1020, 47023 Cesena, Italy
Received 11 October 2001; accepted 10 November 2003
Abstract Snack-like products were obtained by extrusion-cooking of chestnut–rice flour blend-based doughs, by forming the extruded dough in pellets and then baking them in a toaster, in order to obtain adequate puffing. The effects of chestnut flour content and of extrusion temperature on functional (water adsorption index, water-holding capacity and water solubility index) and physical (density, moisture content and color) properties of the extrudates were investigated. Since chestnuts are particularly rich in sugars, the flour content limited the gelatinization and the expansion of the product, moreover the combined effect of flour content and temperature enhanced the browning reactions. Chestnut flour was found to be suitable for the extrusion-cooking process adopted if properly mixed with rice flour, with 30% chestnut flour percentage processed at 120 °C producing a snack-like product with limited density and browning that was judged good by a sensory panel. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Chestnut; Rice; Flour; Extrusion-cooking; Snacks
1. Introduction Recent data (Adua, 1999) show that chestnut (Castanea sativa M.) on the whole (fruit and wood chestnuts) represents about 15% of Italian woodlands. In Italy, chestnuts are mainly consumed unprocessed, only about a 20% of the production is used by the food industry (Adua, 1999) either as whole fruit or as flour. The transformation of chestnuts into flour is widely practiced in Italy especially for small nuts or nuts with double embryos. Chestnut flour (CF) is obtained by grinding dried chestnuts after the pericarp and the endocarp have been removed (Bounous &
*
Corresponding author. Fax: +39-085-8071509. E-mail address: [email protected] (G. Sacchetti).
0963-9969/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodres.2003.11.009
Giacalone, 1992). CF is employed as a confectionery paste, which is a basic ingredient of Italian and French desserts (Breisch, 1993). Since chestnut cultivation is important for the environment and sustainability of mountain agriculture, there would be an inherent value for small nuts if a market existed for CF-based products. Studies on CF functional properties in relation to extrusion-cooking processes were conducted (Pinnavaia, Lerici, & Moscatti, 1984; Pinnavaia, Pizzirani, & Papotto, 1995; Silva, Choupina, Sousa, & Beir~ao da Costa, 1994), and the results indicated that CF might be used in the production of new food-stuffs obtained through extrusion-cooking. Extrusion-cooking technology is widely applied to the production of cereal-based snack-like products and it is recommended as being a shorter and more flexible process when compared to others (Harper, 1981). The
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use of CF as a substitute of cereal flours could improve on the nutritional value of products, in fact even if chestnuts show a lower protein content than cereal grains their proteins present peculiar nutritional characteristics: globulins are the main storage proteins and the albumin content is relatively high (accounting for nearly 20%). Aminoacid composition of chestnut globulins shows high similarity to the 11S globulins from leguminous seeds, likewise relatively high contents of albumins were observed in some legumes. Lysine and threonine content is high in chestnut proteins, methionine being the limiting amino acid (Collada, Casado, Barber, Caleya, & Aragoncillo, 1984), moreover chestnuts were found to have a considerable quantity of c-amino butiric acid (Tixier & Desmaison, 1980). Chestnut flour presents also appreciable levels of dietary fibre, vitamin E and B group vitamins (Salvini, Parpinel, Gnagnarella, Maisonneuve, & Turrini, 1998). This research was conducted in order to study the effect of some process variables on the functional and physical properties of a snack-like extruded product obtained using an unconventional ingredient such as CF. CF was shown to be suitable for the extrusion cooking process only when mixed with other flours (Pinnavaia et al., 1984; Silva et al., 1994) because of its limited tendency to expand and its high sugar content that could promote the non-enzymatic browning (NEB) reaction. In fact the process conditions used in extrusion cooking (high temperatures in combination with shear strain and low water content) are known to favour the Maillard reaction (Camire, Camire, & Krumhar, 1990). The objective of this study was to investigate the individual and combined effects of extrusion temperature and CF content on the physical and functional properties of a snack-like product based on a chestnut–rice blend. The choice of rice flour was due to its bland taste that should not cover the typical flavour of chestnut, its low protein content that could limit the NEB reaction rate and its good capacity of expansion. Doughs obtained from different blends of rice and CF were extruded by a single screw extruder, formed, dried and toasted. In order to investigate the effects of the CF content in the blend and of the extrusion temperature on the functional properties of the products, water adsorption index (WAI), water solubility index (WSI) and water-holding capacity (WHC) were tested. Apparent bulk density, moisture content and color were evaluated in order to study the effect of the considered process variables on the final product quality. Finally, the snack-like products were submitted to the judgement of 30 untrained panelists who were invited to express their preference according to hardness, chestnut flour taste and overall judgement of the products.
2. Materials and methods 2.1. Materials Chestnut flour, obtained by milling a local chestnut cultivar (var. Pastinese) that grows in the area of Zocca (Modena, Italy), and commercial rice flour marketed by ADEA (Busto Arsizio, VA, Italy) were used for this study. The CF was about three months old and was stored in refrigerated condition before use. Flour mesh size was <300 lm. Three different blends indicated by the letters A, B and C were prepared by mixing different proportions of CF (20%, 30% and 40%, respectively, for A, B and C blends) and 2% NaCl with rice flour (calculated to difference). A dry mixing process was performed for 10 min using a FEN (New Food Engineering, Vicenza, Italy) twin shaft batch mixer. The maximum level of 40% CF content was set according to preliminary studies (Pinnavaia et al., 1984), while the minimum level of 20% was chosen in order to maintain the chestnut flour flavour. A 2% salt content was introduced in order to enhance product flavour. 2.2. Analytical tests Chemical analyses (protein, starch, sugars, fat, ash and fiber) were performed according to AOAC (1990) methods. Moisture content of flour was measured by gravimetrical method. All reagents were of analytical grade. Moisture of pellets was measured by a Sartorius (Goettingen, Germany) Thermocontrol thermic balance, daily calibrated comparing values to those obtained using AOAC method. Compositional data are reported in Table 1. 2.3. Extruder A FEN (Vicenza, Italy), mod. HTE65, single-screw pilot extruder was employed for this study. This model had a barrel length of 1365 mm and a length to diameter
Table 1 Chemical composition of the chestnut and rice flours
Moisture (%) Protein Starch Sugars Reducing sugars Crude fat Ash Fiber a
% on dry, total basis. % on as is basis. N 5.3. ** N 5.7. b
Chestnut flour
Rice flour
7.14 0.11 6.92 0.24a 50.65 0.32a 32.64 0.57a 1.79 0.04a 2.05 0.04a 2.77 0.01a 4.19 0.33a
14 9b 73.2b – – 1b 0.6b 0.2b
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ratio of 21. The screw was a FEN 65B model with a compression ratio of 1.6:1. The heating system was in four stages with a pre-heating zone, two heating zone and a cooling zone. The extruder was equipped with a drawplate which had a 83-mm diameter ring die with a 0.5-mm span. The die plate was equipped with a cutting device in order to operate the opening of the extruded dough sheet. 2.4. Experimental design and conditions The experimental design was a factorial design with three levels and two variables where CF content and extrusion temperature were taken as independent variables. Three extrusion processes were carried out for each combination of the two variables. The blends with three different CF contents (20%, 30% and 40%) were extruded at 90, 105 and 120 °C. Screw speed was set to 80 rpm and feed moisture content was of 35% according to a previous study (Pinnavaia et al., 1995). Screw speed was set constant because, according to previous trials and other researches (Silva et al., 1994), it did not show to significantly affect product density and color. Feed moisture was adjusted by means of a Mono pump. The input feed rate was of 25 kg h1 and pressure behind the die reached 2.5–3 MPa. The extruded dough sheet (0.7-mm thick) was stamped and formed into 0.5-mm thick hexagonalshaped pellets. The stamping process was conduced using an erthacetal rotative stamp with irregular hexagonal matrices (major axe 30 mm and minor axe 20 mm). The pellets were dried to 10% moisture content in an air circulation drier at 50% RH, at a drying temperature of 50 °C. In order to obtain puffed snacks, the pellets were finally baked in a FEN mod.TO-10 toaster with two different heating zones. The toasting process was run at 143 °C for a time of 11 s in the pre-heating zone and at 220 °C for a time of 22 s in the expansion zone. Air speed in the expansion zone was set to 7 ms1 .
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(WHC) was measured according to the method proposed by Pinnavaia and Pizzirani (1998). Product samples were ground to <0.5 mm diameter using a Fritsch (Idar-Oberstein, Germany) Pulverisette 14 mill equipped with a No. 40 sieve. Apparent bulk density of the products, as defined by Harper (1981), was determined on whole products by measuring the weight of a constant volume (1 litre) of product. Color was measured on whole products with a Chromameter II reflectance mod.CR110 tristimulus colorimeter (Minolta, Japan), using the CIELAB color space and the standard C illuminant. The colorimeter was calibrated using the white standard calibration plate. Functional and physical tests were performed on puffed snacks. Each determination was carried out in triplicate. 2.7. Sensory evaluations A preliminary product selection was made in order to reduce the number of samples to be submitted to the panel which was made up by untrained judges. Selection was made on the basis of an acceptance test performed by five expert assessors (ISO 8586-2, 1994) specialized in the evaluation of snack products. Selection results were given as: acceptable/not acceptable. Acceptability was assessed on the basis of sensory specifics defined for snack products in the producer quality manual (homogeneity of expansion, presence of dark zones and hardness). A final sensory evaluation was made by a group of 30 untrained judges (25–45 year old males and females) who were invited to evaluate hardness (quantitative rating), chestnut flour flavour (quantitative rating), overall flavour and judgement (hedonic ratings) of products previously selected by the experts. Seven point category scales were adopted and the categories were rated from 1 (very low/dislike) to 7 (very high/like) in order to evaluate the statistical significance of the panel test results.
2.5. Viscoamylograph profiles
2.8. Statistical analysis
A Brabender (Duisburg, Germany) viscoamylograph equipped with standard accessories and 700 cm g sensitivity cartridge was used to determine viscosity profiles. A 10% solids (50 g sample) water suspension was heated at a rate of 1.5 °C min1 from 50 to 95 °C, held at 95 °C for 10 min, then cooled at a rate of )1.5 °C min1 to 50 °C. Water suspension was maintained under constant stirring at 75 rpm as suggested by Rasper (1988).
The response variables were modelled as a function of independent variables according to second-order polynomial models. Data were modelled by multiple regression analysis adopting backward stepwise analysis and only the variables significant at p < 0:01 level were selected for the model construction. The goodness-of-fit of the models was evaluated using the adjusted R2 (Piggot, 1986), the Fisher F test (and the derived p values) and the standard error of estimation (SE). Statistical differences between sensory data were investigated using the Kruskall–Wallis H test and Mann Whitney U test because data were discontinuos (Piggot, 1986). Data were processed using the Statistica for Windows (Statsoft Inc., Tulsa, OK) package.
2.6. Functional and physical tests Water absorption index (WAI) and water solubility index (WSI) were determined using the procedures proposed by Anderson (1982). Water-holding capacity
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3. Results and discussion 3.1. Properties of initial blends The functional properties of the initial blends showed different behaviour when the CF content was increased (Table 2); this fact is due to the high percentage of sugars present in CF, which caused a decrease in the starch to sugar ratio, thus leading to a WAI decrease and WSI increase. The color of the blends tends to turn slightly darker when the CF percentage increased in the initial blend (Table 2). The addition of CF to the initial blend also caused a and b values to increase. This trend can be attributed to the color of the CF in contrast to rice flour, which is almost white. 3.2. Functional properties of snacks The values of the WAI and the WHC indices of puffed snack products as a function of the two independent variables are shown in Fig. 1(a) and (b), respectively. The general regression equations and statistical significance of responses are reported in Table 3. WAI and WHC are referred to as measurments of the degree of starch gelatinization (OwusuAnsah, van de Voort, & Stanley, 1983; Pinnavaia & Pizzirani, 1998). Both indices showed a second-order relation with the CF content of the raw blend. When the CF content is high, low values of WAI and WHC are probably due to the sucrose content of chestnuts. Sucrose, in fact, as well known, has a restrictive effect on the gelatinization process (Wootton & Bamunuarachchi, 1980). This is due to several factors including competition between starch and sucrose for available water, sucrose inhibition of granular starch hydration, and sucrose–starch interaction (Lund, 1984). In the presence of a high sugar content, when starch can not gelatinize due to thermal reaction, there is a tendency for a physical mixture of caramel with starch and starch–sugar complexes to be formed (Tomasik & Jane, 1995). Low values of WAI and WHC were also found in products with low CF content and low temperatures of extrusion (Fig. 1(a) and (b)); this fact could be ascribed to different behaviours of the two employed flours when subjected to thermal treatment. As shown by the
Fig. 1. Response surface diagram showing the effect of chestnut flour content and extrusion temperature on the products WAI (a), WSI (b) and WHC (c).
viscoamylographic profiles reported in Fig. 2, rice flour gelatinization occurs at a higher temperature than that of CF (interval 68–81 versus 66–76 °C), and this could determine a depression of starch gelatinization when blends with a high content of rice flour are processed at the lowest extrusion temperature (90 °C). In the considered blends the gelatinization temperature of rice
Table 2 Functional properties and color parameters of chestnut–rice flour blends Chestnut flour (%)
WAI
WHC
WSI
L
a
b
20 (blend A) 30 (blend B) 40 (blend C)
1.82b 1.93a 1.95a
1.42a 1.41a 1.43a
13.5c 18.01b 21.1a
91.6a 91.1b 90.7c
4.6a 4.6a 4.6a
3.1c 4.2b 4.9a
Means with the same letter are not significantly different at a p 6 0:05 level.
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Table 3 Effects of chestnut flour content and extrusion temperature on the products functional and physical properties Response
Equationa
WAI
Za ¼ 4:797126 0:030173X 2 0:001902Y 2 þ 0:016945XY þ 0:000021Y 3 þ 0:00029X 2 Y 0:000165XY 2 : R2 adj. ¼ 0.997 SE ¼ 0.036 F ¼ 1174
WHC
Zh ¼ 5:78389 þ 0:27350X þ 0:08107Y 0:00253X 2 0:00134XY : R2 adj. ¼ 0.942 SE ¼ 0.139
F ¼ 106:9
Zs ¼ 4:08222 þ 0:81683X þ 0:0576Y 0:00669X 2 : R2 adj. ¼ 0.994 SE ¼ 0.405
F ¼ 664:6
WSI Density
Zd ¼ 830:8970 10:7927X 6:7667Y þ 0:0156X 3 0:00002Y 3 0:0107X 2 Y þ 0:0033XY 2 : R2 adj. ¼ 0.995 SE ¼ 2.180 F ¼ 812:4
Moisture
Zm ¼ 3:174815 0:469X þ 0:163407Y þ 0:007744X 2 0:000914Y 2 : R2 adj. ¼ 0.872 SE ¼ 0.199
F ¼ 45:38
ZL ¼ 76:8222 0:00458XY : R2 adj. ¼ 0.879
F ¼ 182:3
L a b
SE ¼ 1.655
Za ¼ 5:796381 0:005852X 2 0:000514Y 2 þ 0:004416XY : SE ¼ 0.518 R2 adj. ¼ 0.821
F ¼ 40:62
Zb ¼ 53:3394 þ 1:1558Y 0:0166X 2 0:0064Y 2 þ 0:0111XY : SE ¼ 1.090 R2 adj. ¼ 0.869
F ¼ 44:13
General regression equations and significance of responses. Where X is the chestnut flour content, Y the extrusion temperature, R2 adj. the adjusted R2 , SE the standard error of estimation and F the Fisher test F value. * Significant at a p < 0:0001 level. a
Fig. 2. Viscoamylographic profile of chestnut (a) and rice (b) flours at 10% solids level.
flour could be further increased by the presence of sucrose due to the addition of CF. WSI increased as a function of both CF content of the initial blend and process temperature (Fig. 1(c)). The values of all the above-mentioned indices showed a growing trend as the extrusion temperature increased. WAI generally increases along with the increase in extrusion temperature; it has a maximum peak at a certain temperature, after which it decreases, probably due to increased dextrinization (Mercier & Feillet, 1975;
Owusu-Ansah et al., 1983). No maximum WAI peak was observed in the temperature range adopted in this study. The combined effect of extrusion temperature and CF content on WAI value affected the statistical significance of the response surface model (contribution to R2 ¼ 0:171) while WHC values appeared to be proportionally related to the extrusion temperature and no combined effect of extrusion temperature and CF content was observed in the model equation (Table 3). WSI values showed a positive correlation with extrusion temperature (Fig. 1(c)) which can be explained by an increase of water soluble carbohydrate due to starch degradation (Gomez & Aguilera, 1983; Mercier & Feillet, 1975). The WSI increase according to temperature appeared to be independent of the CF content of the dough, suggesting that starch degradation, under given extrusion conditions (low screw speed and relatively low extrusion temperatures), were unaffected by the sugar content. 3.3. Moisture and density Apparent bulk density values of the products are reported in Fig. 3(a) as a function of independent variables. Density data decreased when the extrusion temperature increased due to starch gelatinization. According to Mercier and Feillet (1975) and Case, Hamann, and Schwartz (1992), as gelatinization increases, the volume of extruded products increases and bulk density decreases. In the present study, product density
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Because puffing is attributed to both gaseous expansion of water in the product and the degree of gelatinization (Harper, 1981) the residual moisture content was modelled as a function of independent variables (Table 3). As shown in Fig. 3(b), products with intermediate CF and extruded at a high temperature, which showed higher gelatinization degree and lower density, retained the lowest moisture after puffing. By increasing the extrusion temperature, the product moisture showed a significant decrease in relation to density. 3.4. Color The model equations accounting for the individual and combined effect of CF content and extrusion temperature on product color parameters are reported in Table 3. The response surfaces of L and a parameters (referred to as Maillard reaction indices) are reported in Fig. 4(a) and (b), respectively. The interactive effects of the two independent variables are a determining factor in testing the statistical significance of the models (R2 contribution are 0.879, 0.242 and 0.262, respectively, for L , a and b indices). The snack’s lightness (L ) tends to decrease with the increase in CF content in the initial blend, as evidenced by the initial blend color; this trend Fig. 3. Response surface diagram showing the effect of chestnut flour content and extrusion temperature on the products bulk density (a) and moisture content (b).
showed a negative correlation with gelatinization indices (r ¼ 0:834 and 0.875 for WAI and WHC, respectively). Density values were generally lower for products with an intermediate CF content. Products with low CF content (blend A-based) presented generally higher density than products with low CF content (blend B-based); as previously discussed this could be due to a lesser degree of gelatinization determined by the higher gelatinization temperature of rice flour. Increasing the heating temperature, while keeping the treatment time constant, increases gelatinization (Lund, 1984), thus reducing the difference between density values of blend A and blend B-based products. At 120 °C, the blend A-based product showed lower density values than blend B-based products. This is probably due to the depressive effect of blend B’s higher sucrose content on the degree of gelatinization. Blend C-based products, which had the higher CF content, also presented the highest apparent bulk density values. This is due to the high sucrose content of this blend. The reduction in expansion and density increase due to sugar addition was discussed by other authors and attributed to a weaker bubble wall caused both by a reduction in the starch polymer content and reduced entanglements between starch polysaccharide because of the reduction in starch conversion (Carvalho & Mitchell, 2000).
Fig. 4. Response surface diagram showing the effect of chestnut flour content and extrusion temperature on the products L (a) and a (b) chromatic parameters.
G. Sacchetti et al. / Food Research International 37 (2004) 527–534
is due to the darkening effect determined CF addition. Extrusion temperature appeared to have little effect on the product L and a values when low CF content blends were used. On the other hand, when the CF content of the initial blend was increased, the extrusion temperature increase caused the product browning (Fig. 4(a) and (b)). This fact could be ascribed to CF’s high reducing sugars content, which could promote color changes due to Maillard reaction development according to extrusion temperature. CF content and extrusion temperature showed a negative quadratic effect on the product’s a and b parameters with an initial increase and a subsequent decrease. Analogue changes of the a and b parameters due to the Maillard reaction development were observed by other authors (MacDougall & Granov, 1998). 3.5. Sensory evaluation Only the products extruded at 120 °C were considered acceptable by the preliminary assessment performed by an acceptability test. Data of a second acceptance test are reported in Table 4. The results show that it can be assumed that all selected products showed a distinctive chestnut flavour. Hardness increased with the increase of CF content of the initial blend. Hardness values showed a positive correlation with product density (r ¼ 0:997), as it was also pointed out by other authors (Case et al., 1992; Mercier & Feillet, 1975). Products obtained adopting the intermediate CF content showed a higher hedonic rating of the flavour, but the product with higher CF content presented a slightly bitter taste according to most panelists. On the basis of color analysis results, the bitter taste can be related to off-flavour development due to the Maillard reactions (Lignert, 1990). The blend B-based sample received a better overall evaluation than blend C-based sample, which had a hard consistency along with a slightly bitter taste. The results of overall evaluation data showed that it was not possible to differentiate the A sample from the others. Table 4 Median values and statistical analysis of sensory attributes evaluated on products having different chestnut flour content Chestnut flour content
Intensity ratings Chestnut flavour
Hardness
20% (blend A) 30% (blend B) 40% (blend C)
4.0b 6.0a 6.0a
4.0c 5.0b 6.0a
533
4. Conclusions The results obtained from this study confirmed that CF is suitable for the extrusion cooking process only if properly mixed with other flours due to its high sugar content, which has a restrictive effect on product gelatinization and limits product expansion. Moreover, as suggested by other authors (Carvalho & Mitchell, 2000), high sucrose concentrations increase the viscosity of the dough; this could be a limiting factor in single screw extrusion processing (Huber, 1991). Due to its high reducing sugar content, the use of CF was also shown to be limited by high extrusion temperatures which could enhance the Maillard reaction rate, causing the occurrence of browning phenomena and flavour development that could be desirable or undesirable depending on their extent. Among the experimental conditions used in the present study, a chestnut–rice flour blend having a 30% CF content extruded at a 120 °C temperature showed the best performance, resulting in a well-gelatinized and well-expanded snack-like product with good sensory attributes. CF could be used as a functional ingredient in the formulation of snack products, in fact, when added to cereal-based mixtures, it could improve nutritional value (high content in fibre, lysine and methionine, c-amino butiric acid, vitamin E and B group vitamins), physical properties (texture, density and color), as well as the sensory characteristics (sweetness and aroma) of extruded products. From a sensory standpoint CF has a pleasant taste which grants its appreciation by the sweets and candy industries; moreover, as reported in this study, during processing chestnut sugars could enhance the Maillard reaction occurrence, thus improving the product’s biscuit-like and roasted aroma. These sensory characteristics were also shown to fit well with other extruded products such as RTE breakfast cereals (Sacchetti & Pinnavaia, 1999).
Acknowledgements Extrusion-cooking processes were conduced in the R & Dlaboratories of MAFIN S.p.a. (Galliera Veneta, PD Italy).
Hedonic ratings
Flavour
Overall judgement
4.0b 6.0a 4.0b
5.0ab 5.0a 4.0b
Values with the same letter are not significantly different at a p 6 0:01 level. * Attribute significant at p 6 0:01 level.
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Mercier, C., & Feillet, P. (1975). Modification of carbohydrate components by extrusion-cooking of cereal products. Cereal Chemistry, 52(3), 283–297. Owusu-Ansah, J., van de Voort, F. R., & Stanley, D. W. (1983). Physicochemical changes in cornstarch as a function of extrusion variables. Cereal Chemistry, 60(4), 319–324. Piggot, J. R. (1986). Statistical procedures in food research (pp. 52–56, 86–101). New York: Elsevier Applied Science. Pinnavaia, G. G., & Pizzirani, S. (1998). Evaluation of the degree of gelatinization by water holding capacity. Starch/St€arke, 50(2–3), 64–67. Pinnavaia, G. G., Lerici, C. R., & Moscatti, P. (1984). Proprieta funzionali della farina di castagne in relazione ai processi di cottura-estrusione. Tecnica Molitoria, 35(10), 725– 732. Pinnavaia, G. G., Pizzirani, S., & Papotto, E. G. (1995). Studio di fattibilita produttiva di un prodotto estruso a base di farina di castagne. Industrie Alimentari, 34(341), 977–984, 987. Rasper, V. (1988). Theoretical aspects of amylographology. In C. Shuey & K. H. Tipples (Eds.), The amylograph handbook (pp. 1–6). St. Paul: AACC. Sacchetti, G., & Pinnavaia, G. G. (1999). A ready-to-eat chestnut flour based breakfast cereal. Production and optimization. In G. Salesses (Ed.), Proceedings of the 2nd international symposium on chestnut. Acta Horticulturae, 494, 61–68. Salvini, S., Parpinel, M., Gnagnarella, P., Maisonneuve, P., & Turrini, A. (1998). Banca dati di composizione degli alimenti per studi epidemiologici in Italia (pp. 370). Milano: Istituto Europeo di Oncologia. Silva, F., Choupina, I., Sousa, M. N., & Beir~ao da Costa, M. L. (1994). Extrusion of Castanea sativa. In T. Yano, R. Matsuno, & K. Nakamura (Eds.), Proceeding of 6th international congress on engineering and food (pp. 882–884). Tokyo: Blackie Academic. Tixier, M., & Desmaison, A. M. (1980). Relation metabolique entre l’arginine et l’acide gamma aminobutirique dans le fruit de Castanea sativa. Phytochemistry, 19, 1643–1646. Tomasik, P., & Jane, J. (1995). Reaction of starch and cellulose with products of thermal decomposition of mono- and disaccharides. Starch/St€arke, 47(1), 24–29. Wootton, M., & Bamunuarachchi, A. (1980). Application of differential scanning calorimetry to starch gelatinization. III. Effect of sucrose and sodium chloride. Starch/St€arke, 32(4), 126–129.
Effects of extrusion temperature and feed composition on the functional, physical and sensory properties of chestnut and rice flour-based snack-like products G. Sacchetti b
a,*
, G.G. Pinnavaia b, E. Guidolin c, M. Dalla Rosa
d
a Dipartimento di Scienze degli Alimenti, Universita degli Studi di Teramo, Via Spagna 1, Mosciano Stazione, 64023 Teramo, Italy Dipartimento di Protezione e Valorizzazione Agro-Alimentare, Universita degli Studi di Bologna, Sede di Cesena, Via Ravennate 1020, 47023 Cesena, Italy c MAFIN S.p.a. Strada degli Alberi, 7, 35015 Galliera Veneta (PD), Italy d Dipartimento di Scienze degli Alimenti, Universita degli Studi di Bologna, Sede di Cesena, Via Ravennate 1020, 47023 Cesena, Italy
Received 11 October 2001; accepted 10 November 2003
Abstract Snack-like products were obtained by extrusion-cooking of chestnut–rice flour blend-based doughs, by forming the extruded dough in pellets and then baking them in a toaster, in order to obtain adequate puffing. The effects of chestnut flour content and of extrusion temperature on functional (water adsorption index, water-holding capacity and water solubility index) and physical (density, moisture content and color) properties of the extrudates were investigated. Since chestnuts are particularly rich in sugars, the flour content limited the gelatinization and the expansion of the product, moreover the combined effect of flour content and temperature enhanced the browning reactions. Chestnut flour was found to be suitable for the extrusion-cooking process adopted if properly mixed with rice flour, with 30% chestnut flour percentage processed at 120 °C producing a snack-like product with limited density and browning that was judged good by a sensory panel. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Chestnut; Rice; Flour; Extrusion-cooking; Snacks
1. Introduction Recent data (Adua, 1999) show that chestnut (Castanea sativa M.) on the whole (fruit and wood chestnuts) represents about 15% of Italian woodlands. In Italy, chestnuts are mainly consumed unprocessed, only about a 20% of the production is used by the food industry (Adua, 1999) either as whole fruit or as flour. The transformation of chestnuts into flour is widely practiced in Italy especially for small nuts or nuts with double embryos. Chestnut flour (CF) is obtained by grinding dried chestnuts after the pericarp and the endocarp have been removed (Bounous &
*
Corresponding author. Fax: +39-085-8071509. E-mail address: [email protected] (G. Sacchetti).
0963-9969/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodres.2003.11.009
Giacalone, 1992). CF is employed as a confectionery paste, which is a basic ingredient of Italian and French desserts (Breisch, 1993). Since chestnut cultivation is important for the environment and sustainability of mountain agriculture, there would be an inherent value for small nuts if a market existed for CF-based products. Studies on CF functional properties in relation to extrusion-cooking processes were conducted (Pinnavaia, Lerici, & Moscatti, 1984; Pinnavaia, Pizzirani, & Papotto, 1995; Silva, Choupina, Sousa, & Beir~ao da Costa, 1994), and the results indicated that CF might be used in the production of new food-stuffs obtained through extrusion-cooking. Extrusion-cooking technology is widely applied to the production of cereal-based snack-like products and it is recommended as being a shorter and more flexible process when compared to others (Harper, 1981). The
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use of CF as a substitute of cereal flours could improve on the nutritional value of products, in fact even if chestnuts show a lower protein content than cereal grains their proteins present peculiar nutritional characteristics: globulins are the main storage proteins and the albumin content is relatively high (accounting for nearly 20%). Aminoacid composition of chestnut globulins shows high similarity to the 11S globulins from leguminous seeds, likewise relatively high contents of albumins were observed in some legumes. Lysine and threonine content is high in chestnut proteins, methionine being the limiting amino acid (Collada, Casado, Barber, Caleya, & Aragoncillo, 1984), moreover chestnuts were found to have a considerable quantity of c-amino butiric acid (Tixier & Desmaison, 1980). Chestnut flour presents also appreciable levels of dietary fibre, vitamin E and B group vitamins (Salvini, Parpinel, Gnagnarella, Maisonneuve, & Turrini, 1998). This research was conducted in order to study the effect of some process variables on the functional and physical properties of a snack-like extruded product obtained using an unconventional ingredient such as CF. CF was shown to be suitable for the extrusion cooking process only when mixed with other flours (Pinnavaia et al., 1984; Silva et al., 1994) because of its limited tendency to expand and its high sugar content that could promote the non-enzymatic browning (NEB) reaction. In fact the process conditions used in extrusion cooking (high temperatures in combination with shear strain and low water content) are known to favour the Maillard reaction (Camire, Camire, & Krumhar, 1990). The objective of this study was to investigate the individual and combined effects of extrusion temperature and CF content on the physical and functional properties of a snack-like product based on a chestnut–rice blend. The choice of rice flour was due to its bland taste that should not cover the typical flavour of chestnut, its low protein content that could limit the NEB reaction rate and its good capacity of expansion. Doughs obtained from different blends of rice and CF were extruded by a single screw extruder, formed, dried and toasted. In order to investigate the effects of the CF content in the blend and of the extrusion temperature on the functional properties of the products, water adsorption index (WAI), water solubility index (WSI) and water-holding capacity (WHC) were tested. Apparent bulk density, moisture content and color were evaluated in order to study the effect of the considered process variables on the final product quality. Finally, the snack-like products were submitted to the judgement of 30 untrained panelists who were invited to express their preference according to hardness, chestnut flour taste and overall judgement of the products.
2. Materials and methods 2.1. Materials Chestnut flour, obtained by milling a local chestnut cultivar (var. Pastinese) that grows in the area of Zocca (Modena, Italy), and commercial rice flour marketed by ADEA (Busto Arsizio, VA, Italy) were used for this study. The CF was about three months old and was stored in refrigerated condition before use. Flour mesh size was <300 lm. Three different blends indicated by the letters A, B and C were prepared by mixing different proportions of CF (20%, 30% and 40%, respectively, for A, B and C blends) and 2% NaCl with rice flour (calculated to difference). A dry mixing process was performed for 10 min using a FEN (New Food Engineering, Vicenza, Italy) twin shaft batch mixer. The maximum level of 40% CF content was set according to preliminary studies (Pinnavaia et al., 1984), while the minimum level of 20% was chosen in order to maintain the chestnut flour flavour. A 2% salt content was introduced in order to enhance product flavour. 2.2. Analytical tests Chemical analyses (protein, starch, sugars, fat, ash and fiber) were performed according to AOAC (1990) methods. Moisture content of flour was measured by gravimetrical method. All reagents were of analytical grade. Moisture of pellets was measured by a Sartorius (Goettingen, Germany) Thermocontrol thermic balance, daily calibrated comparing values to those obtained using AOAC method. Compositional data are reported in Table 1. 2.3. Extruder A FEN (Vicenza, Italy), mod. HTE65, single-screw pilot extruder was employed for this study. This model had a barrel length of 1365 mm and a length to diameter
Table 1 Chemical composition of the chestnut and rice flours
Moisture (%) Protein Starch Sugars Reducing sugars Crude fat Ash Fiber a
% on dry, total basis. % on as is basis. N 5.3. ** N 5.7. b
Chestnut flour
Rice flour
7.14 0.11 6.92 0.24a 50.65 0.32a 32.64 0.57a 1.79 0.04a 2.05 0.04a 2.77 0.01a 4.19 0.33a
14 9b 73.2b – – 1b 0.6b 0.2b
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ratio of 21. The screw was a FEN 65B model with a compression ratio of 1.6:1. The heating system was in four stages with a pre-heating zone, two heating zone and a cooling zone. The extruder was equipped with a drawplate which had a 83-mm diameter ring die with a 0.5-mm span. The die plate was equipped with a cutting device in order to operate the opening of the extruded dough sheet. 2.4. Experimental design and conditions The experimental design was a factorial design with three levels and two variables where CF content and extrusion temperature were taken as independent variables. Three extrusion processes were carried out for each combination of the two variables. The blends with three different CF contents (20%, 30% and 40%) were extruded at 90, 105 and 120 °C. Screw speed was set to 80 rpm and feed moisture content was of 35% according to a previous study (Pinnavaia et al., 1995). Screw speed was set constant because, according to previous trials and other researches (Silva et al., 1994), it did not show to significantly affect product density and color. Feed moisture was adjusted by means of a Mono pump. The input feed rate was of 25 kg h1 and pressure behind the die reached 2.5–3 MPa. The extruded dough sheet (0.7-mm thick) was stamped and formed into 0.5-mm thick hexagonalshaped pellets. The stamping process was conduced using an erthacetal rotative stamp with irregular hexagonal matrices (major axe 30 mm and minor axe 20 mm). The pellets were dried to 10% moisture content in an air circulation drier at 50% RH, at a drying temperature of 50 °C. In order to obtain puffed snacks, the pellets were finally baked in a FEN mod.TO-10 toaster with two different heating zones. The toasting process was run at 143 °C for a time of 11 s in the pre-heating zone and at 220 °C for a time of 22 s in the expansion zone. Air speed in the expansion zone was set to 7 ms1 .
529
(WHC) was measured according to the method proposed by Pinnavaia and Pizzirani (1998). Product samples were ground to <0.5 mm diameter using a Fritsch (Idar-Oberstein, Germany) Pulverisette 14 mill equipped with a No. 40 sieve. Apparent bulk density of the products, as defined by Harper (1981), was determined on whole products by measuring the weight of a constant volume (1 litre) of product. Color was measured on whole products with a Chromameter II reflectance mod.CR110 tristimulus colorimeter (Minolta, Japan), using the CIELAB color space and the standard C illuminant. The colorimeter was calibrated using the white standard calibration plate. Functional and physical tests were performed on puffed snacks. Each determination was carried out in triplicate. 2.7. Sensory evaluations A preliminary product selection was made in order to reduce the number of samples to be submitted to the panel which was made up by untrained judges. Selection was made on the basis of an acceptance test performed by five expert assessors (ISO 8586-2, 1994) specialized in the evaluation of snack products. Selection results were given as: acceptable/not acceptable. Acceptability was assessed on the basis of sensory specifics defined for snack products in the producer quality manual (homogeneity of expansion, presence of dark zones and hardness). A final sensory evaluation was made by a group of 30 untrained judges (25–45 year old males and females) who were invited to evaluate hardness (quantitative rating), chestnut flour flavour (quantitative rating), overall flavour and judgement (hedonic ratings) of products previously selected by the experts. Seven point category scales were adopted and the categories were rated from 1 (very low/dislike) to 7 (very high/like) in order to evaluate the statistical significance of the panel test results.
2.5. Viscoamylograph profiles
2.8. Statistical analysis
A Brabender (Duisburg, Germany) viscoamylograph equipped with standard accessories and 700 cm g sensitivity cartridge was used to determine viscosity profiles. A 10% solids (50 g sample) water suspension was heated at a rate of 1.5 °C min1 from 50 to 95 °C, held at 95 °C for 10 min, then cooled at a rate of )1.5 °C min1 to 50 °C. Water suspension was maintained under constant stirring at 75 rpm as suggested by Rasper (1988).
The response variables were modelled as a function of independent variables according to second-order polynomial models. Data were modelled by multiple regression analysis adopting backward stepwise analysis and only the variables significant at p < 0:01 level were selected for the model construction. The goodness-of-fit of the models was evaluated using the adjusted R2 (Piggot, 1986), the Fisher F test (and the derived p values) and the standard error of estimation (SE). Statistical differences between sensory data were investigated using the Kruskall–Wallis H test and Mann Whitney U test because data were discontinuos (Piggot, 1986). Data were processed using the Statistica for Windows (Statsoft Inc., Tulsa, OK) package.
2.6. Functional and physical tests Water absorption index (WAI) and water solubility index (WSI) were determined using the procedures proposed by Anderson (1982). Water-holding capacity
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3. Results and discussion 3.1. Properties of initial blends The functional properties of the initial blends showed different behaviour when the CF content was increased (Table 2); this fact is due to the high percentage of sugars present in CF, which caused a decrease in the starch to sugar ratio, thus leading to a WAI decrease and WSI increase. The color of the blends tends to turn slightly darker when the CF percentage increased in the initial blend (Table 2). The addition of CF to the initial blend also caused a and b values to increase. This trend can be attributed to the color of the CF in contrast to rice flour, which is almost white. 3.2. Functional properties of snacks The values of the WAI and the WHC indices of puffed snack products as a function of the two independent variables are shown in Fig. 1(a) and (b), respectively. The general regression equations and statistical significance of responses are reported in Table 3. WAI and WHC are referred to as measurments of the degree of starch gelatinization (OwusuAnsah, van de Voort, & Stanley, 1983; Pinnavaia & Pizzirani, 1998). Both indices showed a second-order relation with the CF content of the raw blend. When the CF content is high, low values of WAI and WHC are probably due to the sucrose content of chestnuts. Sucrose, in fact, as well known, has a restrictive effect on the gelatinization process (Wootton & Bamunuarachchi, 1980). This is due to several factors including competition between starch and sucrose for available water, sucrose inhibition of granular starch hydration, and sucrose–starch interaction (Lund, 1984). In the presence of a high sugar content, when starch can not gelatinize due to thermal reaction, there is a tendency for a physical mixture of caramel with starch and starch–sugar complexes to be formed (Tomasik & Jane, 1995). Low values of WAI and WHC were also found in products with low CF content and low temperatures of extrusion (Fig. 1(a) and (b)); this fact could be ascribed to different behaviours of the two employed flours when subjected to thermal treatment. As shown by the
Fig. 1. Response surface diagram showing the effect of chestnut flour content and extrusion temperature on the products WAI (a), WSI (b) and WHC (c).
viscoamylographic profiles reported in Fig. 2, rice flour gelatinization occurs at a higher temperature than that of CF (interval 68–81 versus 66–76 °C), and this could determine a depression of starch gelatinization when blends with a high content of rice flour are processed at the lowest extrusion temperature (90 °C). In the considered blends the gelatinization temperature of rice
Table 2 Functional properties and color parameters of chestnut–rice flour blends Chestnut flour (%)
WAI
WHC
WSI
L
a
b
20 (blend A) 30 (blend B) 40 (blend C)
1.82b 1.93a 1.95a
1.42a 1.41a 1.43a
13.5c 18.01b 21.1a
91.6a 91.1b 90.7c
4.6a 4.6a 4.6a
3.1c 4.2b 4.9a
Means with the same letter are not significantly different at a p 6 0:05 level.
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531
Table 3 Effects of chestnut flour content and extrusion temperature on the products functional and physical properties Response
Equationa
WAI
Za ¼ 4:797126 0:030173X 2 0:001902Y 2 þ 0:016945XY þ 0:000021Y 3 þ 0:00029X 2 Y 0:000165XY 2 : R2 adj. ¼ 0.997 SE ¼ 0.036 F ¼ 1174
WHC
Zh ¼ 5:78389 þ 0:27350X þ 0:08107Y 0:00253X 2 0:00134XY : R2 adj. ¼ 0.942 SE ¼ 0.139
F ¼ 106:9
Zs ¼ 4:08222 þ 0:81683X þ 0:0576Y 0:00669X 2 : R2 adj. ¼ 0.994 SE ¼ 0.405
F ¼ 664:6
WSI Density
Zd ¼ 830:8970 10:7927X 6:7667Y þ 0:0156X 3 0:00002Y 3 0:0107X 2 Y þ 0:0033XY 2 : R2 adj. ¼ 0.995 SE ¼ 2.180 F ¼ 812:4
Moisture
Zm ¼ 3:174815 0:469X þ 0:163407Y þ 0:007744X 2 0:000914Y 2 : R2 adj. ¼ 0.872 SE ¼ 0.199
F ¼ 45:38
ZL ¼ 76:8222 0:00458XY : R2 adj. ¼ 0.879
F ¼ 182:3
L a b
SE ¼ 1.655
Za ¼ 5:796381 0:005852X 2 0:000514Y 2 þ 0:004416XY : SE ¼ 0.518 R2 adj. ¼ 0.821
F ¼ 40:62
Zb ¼ 53:3394 þ 1:1558Y 0:0166X 2 0:0064Y 2 þ 0:0111XY : SE ¼ 1.090 R2 adj. ¼ 0.869
F ¼ 44:13
General regression equations and significance of responses. Where X is the chestnut flour content, Y the extrusion temperature, R2 adj. the adjusted R2 , SE the standard error of estimation and F the Fisher test F value. * Significant at a p < 0:0001 level. a
Fig. 2. Viscoamylographic profile of chestnut (a) and rice (b) flours at 10% solids level.
flour could be further increased by the presence of sucrose due to the addition of CF. WSI increased as a function of both CF content of the initial blend and process temperature (Fig. 1(c)). The values of all the above-mentioned indices showed a growing trend as the extrusion temperature increased. WAI generally increases along with the increase in extrusion temperature; it has a maximum peak at a certain temperature, after which it decreases, probably due to increased dextrinization (Mercier & Feillet, 1975;
Owusu-Ansah et al., 1983). No maximum WAI peak was observed in the temperature range adopted in this study. The combined effect of extrusion temperature and CF content on WAI value affected the statistical significance of the response surface model (contribution to R2 ¼ 0:171) while WHC values appeared to be proportionally related to the extrusion temperature and no combined effect of extrusion temperature and CF content was observed in the model equation (Table 3). WSI values showed a positive correlation with extrusion temperature (Fig. 1(c)) which can be explained by an increase of water soluble carbohydrate due to starch degradation (Gomez & Aguilera, 1983; Mercier & Feillet, 1975). The WSI increase according to temperature appeared to be independent of the CF content of the dough, suggesting that starch degradation, under given extrusion conditions (low screw speed and relatively low extrusion temperatures), were unaffected by the sugar content. 3.3. Moisture and density Apparent bulk density values of the products are reported in Fig. 3(a) as a function of independent variables. Density data decreased when the extrusion temperature increased due to starch gelatinization. According to Mercier and Feillet (1975) and Case, Hamann, and Schwartz (1992), as gelatinization increases, the volume of extruded products increases and bulk density decreases. In the present study, product density
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Because puffing is attributed to both gaseous expansion of water in the product and the degree of gelatinization (Harper, 1981) the residual moisture content was modelled as a function of independent variables (Table 3). As shown in Fig. 3(b), products with intermediate CF and extruded at a high temperature, which showed higher gelatinization degree and lower density, retained the lowest moisture after puffing. By increasing the extrusion temperature, the product moisture showed a significant decrease in relation to density. 3.4. Color The model equations accounting for the individual and combined effect of CF content and extrusion temperature on product color parameters are reported in Table 3. The response surfaces of L and a parameters (referred to as Maillard reaction indices) are reported in Fig. 4(a) and (b), respectively. The interactive effects of the two independent variables are a determining factor in testing the statistical significance of the models (R2 contribution are 0.879, 0.242 and 0.262, respectively, for L , a and b indices). The snack’s lightness (L ) tends to decrease with the increase in CF content in the initial blend, as evidenced by the initial blend color; this trend Fig. 3. Response surface diagram showing the effect of chestnut flour content and extrusion temperature on the products bulk density (a) and moisture content (b).
showed a negative correlation with gelatinization indices (r ¼ 0:834 and 0.875 for WAI and WHC, respectively). Density values were generally lower for products with an intermediate CF content. Products with low CF content (blend A-based) presented generally higher density than products with low CF content (blend B-based); as previously discussed this could be due to a lesser degree of gelatinization determined by the higher gelatinization temperature of rice flour. Increasing the heating temperature, while keeping the treatment time constant, increases gelatinization (Lund, 1984), thus reducing the difference between density values of blend A and blend B-based products. At 120 °C, the blend A-based product showed lower density values than blend B-based products. This is probably due to the depressive effect of blend B’s higher sucrose content on the degree of gelatinization. Blend C-based products, which had the higher CF content, also presented the highest apparent bulk density values. This is due to the high sucrose content of this blend. The reduction in expansion and density increase due to sugar addition was discussed by other authors and attributed to a weaker bubble wall caused both by a reduction in the starch polymer content and reduced entanglements between starch polysaccharide because of the reduction in starch conversion (Carvalho & Mitchell, 2000).
Fig. 4. Response surface diagram showing the effect of chestnut flour content and extrusion temperature on the products L (a) and a (b) chromatic parameters.
G. Sacchetti et al. / Food Research International 37 (2004) 527–534
is due to the darkening effect determined CF addition. Extrusion temperature appeared to have little effect on the product L and a values when low CF content blends were used. On the other hand, when the CF content of the initial blend was increased, the extrusion temperature increase caused the product browning (Fig. 4(a) and (b)). This fact could be ascribed to CF’s high reducing sugars content, which could promote color changes due to Maillard reaction development according to extrusion temperature. CF content and extrusion temperature showed a negative quadratic effect on the product’s a and b parameters with an initial increase and a subsequent decrease. Analogue changes of the a and b parameters due to the Maillard reaction development were observed by other authors (MacDougall & Granov, 1998). 3.5. Sensory evaluation Only the products extruded at 120 °C were considered acceptable by the preliminary assessment performed by an acceptability test. Data of a second acceptance test are reported in Table 4. The results show that it can be assumed that all selected products showed a distinctive chestnut flavour. Hardness increased with the increase of CF content of the initial blend. Hardness values showed a positive correlation with product density (r ¼ 0:997), as it was also pointed out by other authors (Case et al., 1992; Mercier & Feillet, 1975). Products obtained adopting the intermediate CF content showed a higher hedonic rating of the flavour, but the product with higher CF content presented a slightly bitter taste according to most panelists. On the basis of color analysis results, the bitter taste can be related to off-flavour development due to the Maillard reactions (Lignert, 1990). The blend B-based sample received a better overall evaluation than blend C-based sample, which had a hard consistency along with a slightly bitter taste. The results of overall evaluation data showed that it was not possible to differentiate the A sample from the others. Table 4 Median values and statistical analysis of sensory attributes evaluated on products having different chestnut flour content Chestnut flour content
Intensity ratings Chestnut flavour
Hardness
20% (blend A) 30% (blend B) 40% (blend C)
4.0b 6.0a 6.0a
4.0c 5.0b 6.0a
533
4. Conclusions The results obtained from this study confirmed that CF is suitable for the extrusion cooking process only if properly mixed with other flours due to its high sugar content, which has a restrictive effect on product gelatinization and limits product expansion. Moreover, as suggested by other authors (Carvalho & Mitchell, 2000), high sucrose concentrations increase the viscosity of the dough; this could be a limiting factor in single screw extrusion processing (Huber, 1991). Due to its high reducing sugar content, the use of CF was also shown to be limited by high extrusion temperatures which could enhance the Maillard reaction rate, causing the occurrence of browning phenomena and flavour development that could be desirable or undesirable depending on their extent. Among the experimental conditions used in the present study, a chestnut–rice flour blend having a 30% CF content extruded at a 120 °C temperature showed the best performance, resulting in a well-gelatinized and well-expanded snack-like product with good sensory attributes. CF could be used as a functional ingredient in the formulation of snack products, in fact, when added to cereal-based mixtures, it could improve nutritional value (high content in fibre, lysine and methionine, c-amino butiric acid, vitamin E and B group vitamins), physical properties (texture, density and color), as well as the sensory characteristics (sweetness and aroma) of extruded products. From a sensory standpoint CF has a pleasant taste which grants its appreciation by the sweets and candy industries; moreover, as reported in this study, during processing chestnut sugars could enhance the Maillard reaction occurrence, thus improving the product’s biscuit-like and roasted aroma. These sensory characteristics were also shown to fit well with other extruded products such as RTE breakfast cereals (Sacchetti & Pinnavaia, 1999).
Acknowledgements Extrusion-cooking processes were conduced in the R & Dlaboratories of MAFIN S.p.a. (Galliera Veneta, PD Italy).
Hedonic ratings
Flavour
Overall judgement
4.0b 6.0a 4.0b
5.0ab 5.0a 4.0b
Values with the same letter are not significantly different at a p 6 0:01 level. * Attribute significant at p 6 0:01 level.
References AOAC. (1990). Official methods of analysis (14th ed.). Washington: Association of Official Analytical Chemists. Anderson, R. A. (1982). Water absorption and solubility and amylograph characteristics of roll-cooked small grain products. Cereal Chemistry, 59(4), 265–269.
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