Ispitivanje uticaja procesa ekstrudiranja na dobijanje i stabilnost funkcionalnog hraniva za životinje na bazi lanenog semena

Abstract

Cilj istraživanja u okviru ove doktorske disertacije bio je da se ispita uticaj ekstrudiranja na funkcionalno hranivo, čija bi osnovna uloga bila povećanje sadržaja omega-masnih kiselina u ishrani životinja, a naročito α-linolenske kiseline (ALA). Za proizvodnju funkcionalnog hraniva upotrebljeni su laneno seme, kao nosilac funkcionalnih osobina i suncokretova sačma, koja je dodata da se spreči isticanje lanenog ulja tokom ekstrudiranja. Nezavisni parametri ekstrudiranja čiji je uticaj ispitivan bili su: brzina obrtanja puža ekstrudera (240, 360 i 590 o/min), kapacitet punjenja (16, 24 i 32 kg/h), vlaga polaznog materijala (7, 11,5 i 16 %) i ukupna površina otvora na matrici (19,8, 39,6 i 59,4 mm2). Zavisno promenljive karakteristike (odzivi) dobijenog hraniva koje su praćene bile su: sadržaj HCN u hranivu, sadržaj ALA, sadržaj slobodnih masnih kiselina (SMK) i potrošnja energije. Za modelovanje zavisnosti karakteristika hraniva od procesnih parametara ekstrudiranja primenjena je metoda odzivne površine (RSM), a korišćen je Box-Behnken-ov dizajn (BBD) za četiri faktora na tri nivoa. Za svaki od pomenutih odziva definisan je polinom drugog reda i određeni su koeficijenti polinoma, a analizom varijanse potvrđena je tačnost ovih modela. Formirani modeli upotrebljeni su za optimizaciju procesa ekstrudiranja, sa ciljem da se postigne što veća redukcija cijanogenih glikozida u hranivu, uz što viši sadržaj ALA i što niže SMK i potrošnju energije. Da bi se zadovoljili svi postavljeni uslovi optimizacije, proces ekstrudiranja bilo je potrebno izvoditi pod sledećim uslovima: brzina obrtanja puža – 417,41 o/min, kapacitet punjenja – 32 kg/h, vlaga materijala – 13,39 % i ukupna površina otvora na matrici – 19,80 mm2. Ovako dobijeno hranivo pokazalo je nizak sadržaj HCN, čiji je stepen redukcije u odnosu na početnu vrednost iznosio 76,20 %. Sa druge strane, sadržaj ALA smanjen je za svega 0,69 %, što ukazuje da ekstrudiranje nije negativno uticalo na masnokiselinski sastav proizvedenog ko-ekstrudata. Nakon proizvodnje ko-ekstrudata, pristupilo se ispitivanju njegove održivosti. U tu svrhu uzorci su skladišteni u klima komori sa mogućnošću kontrolisanog podešavanja temperature, relativne vlažnosti i cirkulacije vazduha. Za praćenje održivosti proizvoda primenjen je modifikovan Schaal-oven test. Modifikacija metode sastojala se u podešavanju relativne vlažnosti vazduha na konstantnu vrednost od 40 %, što klasičnom metodom nije propisano. Ova vlažnost vazduha odabrana je na osnovu relativne vlažnosti koja je u trenutku eksperimenta izmerena u prostoriji. U cilju ispitivanja uticaja antioksidanasa na oksidativnu stabilnost proizvoda, uzorcima su dodavani komercijalni preparati karvakrol (200 mg/100 g koekstrudata), vitamin E (135 mg/100 g ko-ekstrudata) i smeša ova dva antioksidansa. Za praćenje oksidativnih i hemijskih promena ko-ekstrudata, određivani su peroksidni broj (Pbr), SMK uzorcima su dodavani komercijalni preparati karvakrol (200 mg/100 g koekstrudata), vitamin E (135 mg/100 g i masnokiselinski sastav. Takođe su ispitane mikrobiološke promene u koekstrudatu. Najsnažnije antioksidativno dejstvo u ovom eksperimentu imao je vitamin E, dok smeša vitamina E i karvakrola nije pokazala sinergističko dejstvo. Sastav masnih kiselina se u toku skladištenja nije statistički značajno promenio. Sa druge strane, ekstrudiranje je pokazalo statistički značajan uticaj (p = 0,032) na redukciju ukupnog broja mikroorganizama u hranivu, a najniža vrednost ukupnog broja mikroorganizama (600 cfu/g) zabeležena je u uzorku sa dodatim karvakrolom.

The goal of the research in this thesis was to examine the effect of extrusion on functional feed compound, whose main role was to increase the content of omega-fatty acids in animal nutrition, especially α-linolenic acid (ALA). Flax seed, as the holder of the functional properties, and sunflower meal, as an adsorbent of linseed oil during extrusion, were used for the production of functional feed compound. Independent extrusion parameters studied in the experiment were: extruder screw speed (240, 360 and 590 rpm), loading capacity (16, 24 and 32 kg/h), the moisture content of the starting material (7, 11.5 and 16 % ) and the total die opening’s area (19.8, 39.6 and 59.4 mm2). Dependent variables (responses) of the produced feed compound were: HCN content in coextrudate, ALA content, the content of free fatty acids (FFA) and energy consumption. Response surface methodology (RSM) was applied in order to model mathematical dependence between co-extrudate characteristics and the independent process parameters. The experiments were designed according to Box-Behnken's design (BBD) with four factors, each at three levels. Second-order polynomial equation was developed for each of these responses, and polynomial coefficients were determined. Accuracy of each model was confirmed by analysis of variance (ANOVA). Formed polynomial models were used to optimize the extrusion process, with the aim of achieving high reduction of cyanogenic glycosides in feed compound, the highest content of ALA, as well as low FFA and low energy consumption. Obtained optimal conditions were: extruder srew speed - 417.41 rpm, loading capacity - 32 kg/h, moisture content of starting material - 13.39 % and the total die openings’ area - 19.80 mm2. Functional feed compound produced under these conditions showed a low concentration of HCN, and the degree of HCN reduction was 76.20 % compared to the starting HCN content. On the other hand, the ALA content was reduced by only 0.69 %, indicating that extrusion did not significantly affect the fatty acid composition of the produced co-extrudate. The next step was investigation of stability of produced co-extrudate. For this purpose, the samples were stored in a climate chamber capable of setting temperature, relative humidity and air circulation. Modified Schaal-oven test was used to monitor the stability of the product. Modification of the method consisted in adjusting the relative humidity at a constant value of 40 %, which is not required by a classical method. Such a high humidity was selected based on the relative humidity at a constant value of 40 %, which is not required by a classical method. Such a high humidity was selected based on the relative humidity of air, which was measured in the experimental room at the moment. Commercial carvacrol (200 mg/100g of co-extrudate), vitamin E (135 mg/100 g of co-extrudate) and a mixture of these two antioxidants were added to the samples in order to investigate the influence of antioxidants on the oxidative stability of the product. Peroxide value (PV), FFA and fatty acid composition were determined in order to monitor oxidative and chemical changes in co-extrudate. Microbial changes were also examined in the functional feed compound. The most powerful antioxidant effect in this experiment had vitamin E, and a mixture of vitamin E and carvacrol did not show a synergistic effect. The fatty acid compostion during storage was not significantly changed in any sample. On the other hand, extrusion process showed a statistically significant effect (p = 0.032) on the reduction of total number of microorganisms in feed, and the lowest value of the total number of microorganisms (600 cfu/g) was observed in the sample with added carvacrol.