INFLUENCE OF EXTRUSION PARAMETERS ON NUTRITIONAL AND NON-NUTRITIONAL COMPONENTS OF NEW RYE CULTIVARS

Dorota Gumul¹, Jarosław Korus¹, Bohdan Achremowicz^2
1 Department of Carbohydrates Technology, Agricultural University of Cracow, Poland
² Department of Carbohydrate Technology, University of Agriculture in Cracow, Poland

ABSTRACT

The aim of present work was to asses the influence of extrusion parameters on content of the following nutritional components: protein, lipids, sugars, starch, ash and minerals and also non-nutritional compounds (soluble and non-soluble fraction of dietary fibre, including pentosans and inositol phosphates) in grains of three cultivars of rye: Amilo, Rostockie and Agrikolo. The materials were extrudates from rye grains obtained from three cultivars. The present study determined the chemical composition (nutritional and non-nutritional components) of rye extrudates. Effect of extrusion process was lowering the protein content. The decrease of this component was lower, when higher (20%) initial material moisture was applied than lower (14%). Application of higher moisture of raw material (20%) and lower extrusion process temperature (120°C) negatively influenced on lipids content in rye extrudates. Higher amount of ash was found in rye extrudates obtained at temperature 180°C independently of raw material moisture. The amount of particularly of mineral components depends on parameters of extrusion and rye cultivars. Steeping of rye grains up to 20% and application of lower extrusion temperature (120°C) caused smaller losses in starch content and less intensive increase of sugars during this process. It was noted, that during extrusion of rye grains proportion among soluble and non-soluble fraction of dietary fibre changed in favor of the first one. The effect of extrusion process of rye grains was lowering in content of InsP₆ by 13-98% in comparison to raw material. Independently of rye cultivars extrudates were characterized by significant amount of InsP_3-5, that were not presented in raw material.

Key words: chemical composition, dietary fibre, inositol phosphates, rye extrudates.

INTRODUCTION

Among cereals rye deserves on special attention due to fact, that grains contain higher amount of: soluble fraction of dietary fibre (including pentosans), mineral compounds (Ca, Fe, F), lysine (limiting amino-acid), and also oleic acid in comparison to wheat grains. Moreover rye grains are rich source of B and E groups vitamins [11]. It could be said, that according to present knowledge rye is perfect raw material to produce functional food [5,14,19].

Implementation of extrusion technique in the last few years caused increase in amount of snack type food and cereals breakfast, which are very popular in other countries due to their taste and most of all dietetic value. During extrusion of cereals relationship between soluble and non-soluble fraction of dietary fibre changes in favor to the first one, and for that reason extruded products gain additional dietetic and prophylactic value [20]. It is extremely important, because cereal products are basic source of necessary nutritional and non-nutritional compounds in human nutrition, which consumption prevents of civilization’s diseases development [1,15,29].

The aim of present work was to asses the influence of extrusion parameters on content of the following nutritional components: protein, lipids, sugars, starch, ash and minerals and also non-nutritional compounds (soluble and non-soluble fraction of dietary fibre, including pentosans and inositol phosphates) in grains of three cultivars of rye: Amilo, Rostockie and Agrikolo.

MATERIAL AND METHODS

The materials were extrudates from rye grains obtained from three cultivars of rye: Amilo, Rostockie and Agrikolo. Extrusion was performed in a single screw laboratory extruder Brabender 20 DN, equiped with 3:1 screw and 3 mm dye. Screw speed was maintained at 190 rpm, while two temperature profiles were applied: 80-100-120°C and 120-160-180°C. Prior to the extrusion the moisture of processed rye bran was equilibrated to 14 and 20%.

The following analyses were performed both on raw material (rye grains of three cultivars of rye: Amilo, Rostockie and Agrikolo) and obtained extrudates: protein content according to Kjeldahl in Büchi B 324 (N*5,7), lipids by Soxhlet method in Büchi Universal Extraction System B 811, sugars, dietary fibre and ash carried out according to AOAC [22]. The content of starch, pentosans and inositol phosphates: inositol triphosphate (InsP₃), inositol tetraphosphate (InsP₄), inositol pentaphosphate (InsP₅), inositol hexaphosphate (InsP₆), were evaluated according to ICC standard no 122 [17], Hashimoto et al. [13] and Sandberg and Ahderinne [24], respectivelly.

Macro- and microelements were measured by weighting of 3 g of air dry sample in quartz evaporating dish and incineration for 12 h at 450°C. Then ash was treated with 5 cm³ of HNO₃ (1:2) and carefully vaporized to dryness at heating place. Remnants of carbon in the sample were burnt in furnace for 3 h at 450°C. The residue was treated with 5 cm³ of HCL in order to precipitate silica, vaporized to dryness, again was treated with 5 cm³ of HNO₃ (1:2) and after boiling under cover was filtered through paper filter, washing the deposit with 1% HCl. The content of metals in solution was measured with the means of atomic emission spectrometer (ICP-AES) JY 238 ULTRACE with inductive induced argon plasma (Jobin-Yvon, France).

One factional ANOVA was used to estimate the significance of differences between the obtained results. Calculations were made with a computer program Start Skierniewice 1998.

RESULTS AND DISCUSSION

Contents of proteins, lipids and ash in rye grains and rye extrudates are presented in Table 1. Among all extrudates obtained from grains of three rye cultivars, the lowest content of protein was observed in extrudates from Amilo cultivar, but extrudates obtained from Rostockie and Agrikolo cultivars exhibited the similar content of this nutritive component. Generally, it was stated that extrusion caused lowering the protein content in rye extrudates in comparison to raw material, i.e. grains of Amilo, Rostockie and Agrikolo rye cultivars (Table 1). Protein content in extrudates from Amilo and Rostockie was about 10% lower than content of this compounds in grains of Amilo, and in the case of Rostockie about 14%. The lowest, about 2% decrease in protein content (in comparison to raw material) was detected in extrudates from Agrikolo cultivar. Some exception in this matter was observed in extrudates from Amilo cultivar obtained at 120 and 180°C and 20% initial moisture content, and also extrudate from grains of Agrikolo cultivar extruded at 120°C and 20% initial moisture content (Table 1). Moreover, it was observed, that smaller losses of proteins content in rye extrudates occurred, when higher initial raw material moisture content (20% in place of 14%) was applied, in comparison to unprocessed grains (Table 1). According to Björck and Asp [6] and Asp and Björck [4] the increase in moisture of extruded raw material decreased the degradation, and in consequence the losses of proteins, that confirmed by the results of the present work. In contrary to researches conducted by Pham and Rosario [23] which observed higher losses of protein content with increasing moisture of raw material before extrusion.

Independently of rye cultivars, amount of lipids was lowered, average about 14%, in extrudates in comparison to unprocessed grains (Table 1). It was observed, that decrease of this component was determined by the initial moisture content of rye grains subjected to extrusion process. It was noticed the greater loss of lipids content (in comparison to nonextruded grains) in rye grains steeped to 20% than in the same grains steeped only to 14% (Table 1). Decrease in lipids content in rye extrudates was also conjugated with temperature of process. Applying of lower temperature (120°C) caused greater decrease of this nutritional compound in rye extrudates (Table 1). It could be said, that increased moisture (about 20%) of raw material and lower temperature of extrusion process (120°C) negatively influenced of lipid content in rye extrudates.

Moreover, it was discovered, amount of ash was significantly increased in rye extrudates prepared at 180°C, in comparison to these prepared at lower temperature (120°C). Some exception in this matter was extrudate from the Rostockie prepared at 14% initial moisture level at 120°C (Table 1). Amount of ash remained at constant level in all rye extrudates, independently of rye grains moisture which were subjected to extrusion process, with exception for extrudate obtained from grains of Rostockie cultivar at 120°C, because in this case moisture of raw material was important. But in case of Sotillo and Hettiarachchy [27] researches it was discovered no significant changes in protein and lipid and ash content in plant material after extrusion.

Table 2 presented amounts of selected macro- and microelements in rye grains and rye extrudates. It was found that amount of phosphorus (P) decreased in all investigated extrudates dependently of raw material moisture (higher at 14% moisture) in relation to unprocessed rye grains. The influence of extrusion temperature was significant, because greater decrease of this mineral compound was observed at 120°C than at 180°C. Decrease of magnesium (Mg) content after extrusion was influenced by temperature of the process, and was greater at 120°C, except for extrudates from Rostockie and Agrikolo rye cultivars obtained at initial moisture content of 14% and at 120°C. Extrudates from Amilo cultivar were characterized by constant decrease of calcium (Ca) content (average about 20%), independently of extrusion temperature and initial moisture, in comparison to unprocessed grains. In extrudates obtained from grains the Rostockie decrease of Ca content depend on initial moisture only, in opposition to extrudates from the Agrikolo, where both moisture and temperature of process did not influence unequivocally on decrease of content of this mineral compound. Content of iron (Fe) in extrudates from Amilo cultivar maintained at constant level in comparison to unprocessed grains of this cultivar, in opposition to extrudates from rye of cultivars Rostockie and Agrikolo, where content of Fe increased average about 13% independently of temperature and moisture. Whereas amount of copper (Cu) after extrusion process of rye grains of cultivars Amilo and Rostockie and Agrikolo decreased (about 30%) independently of temperature and moisture in comparison to unprocessed grains of these cultivars of rye. Content of potassium (K) in grains of rye after extrusion process increased in the range of 3-40% in comparison to raw material, and was higher at moisture level 20% than 14%. In case of sodium (Na) it was discovered the decrease of this compound in extrudates obtained from rye cultivars Rostockie and Amilo dependent of process temperature, because higher temperature caused its lower decrease. But in case of extrusion of grains of Agrikolo rye it was observed increase of Na in the range of 30-78%, in comparison to unprocessed grains. In case of extrudates obtained from rye cultivars Rostockie and Agrikolo it was noticed the increase of zinc (Zn) content (about 14% in comparison to raw material), in contrary to Amilo extrudates, where Zn content was unchanged after extrusion. Extrudates from grain of rye cultivars Amilo and Agrikolo were characterized by lower content of manganese (Mn) (about 6% less) in comparison to raw material, and extrudates from rye cultivar Rostockie showed constant content of this compound, independent of extrusion parameters. According to Sotillo and Hettiarachchy [27] after extrusion it was observed decrease in content of such mineral like: P, Ca, Na, Mg in plant material, that was confirmed by this work.

From nutritional point of view carbohydrates could be divided on two groups: digestible and non digestible. Into digestible carbohydrates starch and sugars could be counted, because they were digested and absorbed in small intestine. Content of starch i.e. basic energetic component in cereal grains, and amount of sugars were presented in Table 3. In comparison to raw material, i.e. grains of three rye cultivars, amount of starch decreased by 25% after extrusion in these plant material (Table 3). It could be concluded, that steeping the grains up to 20% moisture level caused smaller losses of starch during extrusion. When higher temperature was used during extrusion (180°C), it caused significantly higher diminishing of this polysaccharide content, in comparison to starch content in extrudates obtained at 120°C (Table 3). According to Moscicki [20] it was caused as consequence of rapid starch hydrolysis under high temperature, and it was confirmed by results of present work. Similar conclusions were obtained Huth et al. [16], because in their researches starch content decreased when extrusion temperature raised. Fact, that after extrusion starch content was diminished is known from previous works [9, 26].

Independently of investigated rye cultivar, amount of sugars increased in the range from 1 to 19% after extrusion at different parameters (initial moisture and temperature), with exception for rye extrudates obtained from raw material steeped up to 20% and extrusion temperature of 120°C (Table 3). Higher content of sugars was discovered in rye extrudates obtained from raw material steeped up to 14% than to 20%. Moreover, it was observed, that amount of sugars increased together temperature of extrusion process (Table 3). It could suggest that lower raw material moisture and higher extrusion temperature influenced the increase of sugars in rye extrudates in comparison to unprocessed rye grains. Probably it was produced by rapidly proceeding starch hydrolysis at this extrusion conditions. In addition, it was observed, that extrudates prepared at raw material moisture of 20% were characterized by lower amount of sugars and higher content of protein in comparison to extrudates prepared at raw material moisture of 14% (Tables 1 and 3). This fact could be explained that higher moisture of raw material subjected to extrusion caused decrease of amount of sugars produced during extrusion and limited protein degradation [21].

In Table 4 are presented the amounts of soluble and non-soluble fraction of dietary fibre as well total dietary fibre in rye extrudates and in raw material (grains of three rye cultivars). Upon analysis of dietary fibre in the investigated extrudates it was concluded, that content of non-soluble fraction was lowered in the range from 8 to 15% during extrusion of rye grains, the most obvious decrease was noted in case of grains of Agrikolo cultivar. It was not observed the unequivocal influence of extrusion process parameters (i.e. temperature and raw material moisture) on decrease of content of non-soluble fraction of dietary fibre in rye grains subjected to this process. In extrudates from Amilo cultivar grains it was found equal decrease of amounts of non-soluble fraction of dietary fibre, independently of extrusion process parameters, while extrudates from Rostockie cultivar the highest decrease in amounts of this fibre (about 13%) was observed in case of extrudates obtained from raw material steeped up to 14%, at 180°C. But extrudates produced from rye grains cultivar Agrikolo exhibited the greatest decrease (about 15%) in content of non-soluble dietary fibre at 120°C and 20% initial material moisture (Table 4). Similarly, extrudates from grains of Amilo cultivar were characterized by constant increase in content of soluble fraction of dietary fibre independently of extrusion process parameters. Whereas in extrudates from Rostockie cultivar grain the greatest increase (about 40%) in this fraction of dietary fibre was observed in case of extrudates obtained from material with initial moisture of 14% at 180°C, where also the highest decrease of non-soluble fraction was observed (Table 4). Analogous, among extrudates from Agrikolo cultivar grains the highest increase in content of soluble dietary fibre was found in extrudates, where the greatest decrease of non-soluble dietary fibre was discovered (Table 4). According to Fornal et al. [10] increase of soluble dietary fibre fraction content was at cost of non-soluble fraction. It was explained by disruption of covalence and non-covalence bounds in carbohydrates during extrusion, that leads to creation of more or less soluble parts of carbohydrates [30]. Steinhart and Rengen [28] in their researches revealed, the effect of extrusion process was increase in soluble dietary fibre content coupled with decrease of non-soluble fraction. In researches conducted by other authors was confirmed the increase of soluble dietary fibre content in cereal extrudates [9, 13, 30]. It was found, that during extrusion of cereals relationship between soluble and non-soluble fraction of dietary fibre was changing in favor of the first fraction, and that fact granted the extruded products with new dietetic and prophylactic properties [21]. But total dietary fibre after extrusion process was slightly diminished, in comparison to unprocessed material, independently of process parameters.

The main constituent of dietary fibre in rye grains are pentosans, and for that reason in this research special attention was devoted to them. Total and non-soluble pentosans content was lowered in the investigated samples in comparison to initial material, in contradiction to soluble fraction (dietetic and prophylactic fraction), which content increased about 50% in all cases (Table 5). It was noted, that soluble pentosans content in all rye extrudates was intensively growing independently of temperature at 14% initial material moisture, in comparison to extrudates obtained at 20%. Moreover it was observed, that all analyzed samples of rye extrudates obtained at raw material moisture of 20% were characterized by greater growth of soluble pentosans at 180°C than 120°C (Table 5). But extrudates produced from grains of rye cultivar Amilo at 14% initial material moisture exhibited higher increase in content of soluble pentosans at temperature of 180°C, in opposition to extrudates obtained at the same moisture of initial material but from grains of cultivars Rostockie and Agrikolo, where the most obvious increase of this compound was found in extrudates prepared at 120°C, in comparison to unprocessed rye grains (Table 5). Similarly the highest decrease of non-soluble pentosans was denoted in extrudates obtained at initial material moisture 14%, in comparison to unprocessed grains independently of process temperature and rye cultivar.

It was discovered, that extrusion of dietary fibre (including pentosans) could change not only proportion between soluble and non-soluble fraction, but also their ability to affect the alimentary tract. Decrease in amount of non-soluble deteriorates ballast creating properties and ability to affect on peristaltic movements of intestines, with simultaneous increase of soluble fraction having health promoting effect on human body and protecting him against so called “civilization diseases” [3, 4, 25, 30]. Moreover according to some authors [4, 20, 30] extrusion process grants to plant material additional dietetic and prophylactic value, that was found in this research.

It was discovered, that content of InsP₆ in rye grains cultivars of Amilo, Rostockie and Agrikolo were 10.4; 11.93; 11.6 µmol*g^-1 d.m. respectively, but InsP_3-5 were not discovered in this plant material (Table 6). These results confirm that rye whole grain are a rich source of inositol hexaphosphate [18, 31]. Extrusion process caused degradation of InsP₆ in extrudates of all cultivars of rye in range (13-98%) in comparison to raw material. Higher loss of amount of InsP₆ was observed in case, when higher extrusion temperature was applied (180°C) and lower moisture (14%) of raw material (Table 6). It may be concluded that lower temperature (120°C) and higher moisture (20%) preserved InsP₆ in plant material. Moreover it was noticed, that as effect of extrusion process was increase of InsP₃ and InsP₄, especially at following extrusion parameters 14% moisture of raw material and 120 and 180°C in comparison to unprocessed material (Table 6). Independently of rye cultivars and extrusion parameters extrudates were characterized by presence of InsP₅, that was not discovered in raw material (Table 6). It may be concluded, that extrusion process negatively influenced InsP₆ content and positively on InsP_3-5 content in plant material. Similar researches conducted by Zieliński et al. [31] revealed 50% decrease in content of InsP₆ in rye grains after extrusion. Moreover it was discovered no increase of InsP_3-5 in rye grain after extrusion process [31].

Extrusion process caused decrease of total inositol phosphates in extrudates of all cultivars of rye in the range from 2% to 75% in comparison to raw material. Higher loss of amount of total inositol phosphates were observed in case the extrudates from the Amilo and the Rostockie, when higher extrusion temperature was applied (180°C) and lower moisture (14%) of raw material (Table 6). Decrease of inositol phosphates content in cereals grains after extrusion was known from previous researches of other authors [2, 9].

CONCLUSIONS

1. Effect of extrusion process was lowering the protein content. The decrease of this component was lower, when higher (20%) initial material moisture was applied than lower (14%).

2. Application of higher moisture of raw material (20%) and lower extrusion process temperature (120°C) negatively influenced on lipids content in rye extrudates.

3. Higher amount of ash was found in rye extrudates obtained at temperature 180°C independently of raw material moisture.

4. Content of P and Mg decreased in all rye extrudates, greater decrease was observed at 120°C than 180°C in comparison to unprocessed grains. It was found, that other mineral components in rye grains (Cu and Ca) was lowered after extrusion process in opposition to Fe, which amount increased independently of initial moisture and extrusion temperature. K content in rye extrudates was about 25% higher than in rye grains before extrusion and this increase was influenced by raw material moisture. Na content was lowered in Rostockie and Amilo rye cultivars and increased twice in the Agrikolo extrudates. But content of such mineral compounds like Zn and Mn was increasing and lowering respectively depending of rye cultivars.

5. Steeping of rye grains up to 20% and application of lower extrusion temperature (120°C) caused smaller losses in starch content during process. The same parameters of extrusion process influenced on less intensive increase of sugars content.

6. It was noted, that during extrusion of cereals proportion among soluble and non-soluble fraction of dietary fibre changed in favor of the first one. Moreover it was observed, that content of these two fractions and total fibre was not unequivocally dependent on extrusion parameters.

7. In general, higher soluble pentosans content in samples of rye extrudates was affected by lower initial material moisture (14%) and lower temperature (120°C).

8. The effect of extrusion process of rye grains was lowering in content of InsP₆ by 13-98% in comparison to raw material, especially when following extrusion parameters were applied: moisture 14% and 180°C temperature. Independently of rye cultivars extrudates were characterized by significant amount of InsP_3-5, that were not presented in raw material.

ACKNOWLEDGEMENTS

This project was suppored by the Polish Ministry of Science (grant PBZ-KBN-094/P06/2003/29).

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Accepted for print: 15.02.2007

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