Quality and durability of fermented goat milk permeat

Arch. Tierz., Dummerstorf 47 (2004) Special Issue, 108-113 Department of Sheep and Goat Breeding1, Department of Animal Physiology and Biochemistry2, Department of Dairy Technology3, August Cieszkowski Agricultural University of Poznań, Poland

DOROTA CAIS-SOKOLIŃSKA1, JACEK WÓJTOWSKI2, JAN PIKUL1 and ROMUALDA DANKÓW1

Quality and durability of fermented goat milk permeat Abstract The purpose of the tests was to evaluate the fermented permeat of goat milk cold stored for 3 weeks. The permeat's characteristics are based on the results determination of basic composition, Ca, Na, K and P content, measurement of selected physical and chemical properties and sensory profile. The permeat obtained as a result of goat milk ultrafiltration was cultured with thermophilous bacteria for milk fermentation. It has been noted that while storing the acidified permeat, its active and potential acidity increases significantly. The value of permeat’s color saturation (r=0.91) decreases proportionally to the storage period. It has been found that as a result of general desirability, the perception of sour taste is mostly affected by turbidity level and the ability of metal taste disappearance. Key Words: goat milk, permeat, shelf-life

Zusammenfassung Titel der Arbeit: Qualität und Haltbarkeit des fermentierten Ziegenmilchpermeates Das Ziel der Untersuchungen war die Beurteilung der Eigenschaften des Ziegenmilchpermeates nach der 3-wöchigen Kühllagerung. Im Permeat wurden die Zusammensetzung, Ca-, Na-, K- und P-Gehalt sowie ausgewählte physikalische-chemische Eigenschaften und sensorisches Profil untersucht. Nach der Ultrafiltration ins Permeat wurden thermophile Sauermilchstarterkulturen zugegeben. Es wurde festgestellt, dass während der Lagerung des gesäuerten Permeates der pH-Wert und 0SH-Säuregrad signifikant zu nahm. Proportional zu der Lagerungszeit nahm der Permeatfarbsättigungsgrad ab (r=0,91). Es ist festgestellt worden, dass für den sensorischen Gesamteindruck der Säure- und Trübegrad sowie die Eigenschaft des Verschwindens des metallischen Geschmackes, den größten Einfluss hatten. Schlüsselwörter: Ziegenmilch, Permeat, Haltbarkeit

Introduction In recent years, goat milk has been more often concentrated using membrane separation processes (MAHDI et al., 1990; DOMAGAŁA and KUPIEC, 2003). The goat milk ultrafiltration process enables to fraction macromolecules and dissolved lawmolecule particles, which is conducive to obtaining the concentrate of specific concentration level and required functional properties as well as permeat as by-product (SRILAORKUL et al., 1991; ŻBIKOWSKA and. ŻBIKOWSKI, 1996). Permeat, upon prior drying, is often a component used in child food-stuffs, deserts and concentrates. It may be also used for milk standardization (HEGGUM, 1999). However, possibilities to use permeat for functional food production are still being sought for. Decreasing the lactose content in permeat and introducing to its composition of milk fermentation bacteria, including strains with pro-biotic properties, additionally increased the nutrition value and digestibility of this substance. The purpose of this study is to assess the quality and lifetime of the fermented goat milk permeat on the basis of its composition, selected physical and chemical as well as sensory properties.

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Material and Methods The tested material was the goat milk permeat obtained under industrial conditions. The reference material was selected goat milk of highest hygienic and cytological quality (DANKÓW et al., 2003). The milk was standardized, pasteurized and thereafter directed to the ultrafiltration module, where it was concentrated to 23% of the dry content. For separation, drilled polypropylene diaphragms Romicon type PM50 with the total area of 2.4 m2. The final pressure of diaphragms’ operation amounted to 1.8 MPa, temperature to 40oC, and the module’s capacity amounted to 870 dm3⋅min1 . The obtained permeat was cultured with a thermophilous bacteria culture with the following stains Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus YC-180 Chr.Hansen. The cultures were added in the form lyophilized Direct Vat Set in the amount of 50 active units, which corresponds to 2% active working starter. The cultured permeat was incubated at the temperature of 43oC for 24 hours until pH under 4 was achieved. The permeat was stored for 21 days at the temperature of 4oC in tight packages of 0.25 dm3 each. The experiment was based on 6 production lots. 4 samples of permeat (n=24) were taken from each lot for testing. Determination of basic chemical composition of milk and permeat was made using standard methods (AOAC 1990). When determining total nitrogen content, the Kjetec System 1026 Distiling Unit Tecator devices was used. Content of macroelements: Ca, Na and K were determined using atomic absorption spectrophotometer, type SP-2900 Pye Unicam, with the background correction in the flame system using adequate cathodic lamps (IDF/ISO, 1992). The phosphorus content was determined using calorimetric method. Active acidity was measured using a pH-meter, type CP-315 Elmetron, fitted with an integrated electrode, type ESAgP-301 W Eurosensor consisting of a glass half-element and saturated chlorosilver half-element. The results of titration acidity were expressed in Soxhleta-Henkla (oSH) degrees (AOAC, 1990). The color of milk and permeat was measured on a reflection basis using a Hitachi U3000 spectrophometer with the layer thickness of 1 cm and C light source. To assess the color in reflected light, the CIELAB system was used, where L* stands for brightness, whereas a* and b* are chromaticity coordinates. The temperature of the measured sample ranged from 22 to 24oC. Basing on the formula: C*=[a2 + b2]0,5, the color saturation was calculated (CIE, 1974). The sensory quality of permeat was tested using the descriptive quantitative analysis. A team of seven qualified and trained assessors tested the sensory profile of the permeat. While making preliminary evaluations, own source of terms describing the properties of tested product were used. The intensity of each factor was marked on the 100 mm scale according to limit determinations. 0-insensible, 10-very intense (Mc EWAN, 1992). The obtained results were subject to statistical analysis using Excel sheets and EAV, ELSQ software. The following were determined: standard error (±SE), linear regression using least squares method and review of the hypothesis at specific significance level p