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Research background. Two methods of milk treatment were used, ultrasound (innovative method) and bactofugation, after which the physicochemical and sensory properties of the milk were examined, with the primary aim of achieving the quality and consistency of the pasteurized milk. Experimental approach. Ultrasound power of 200 and 400 W and frequency of 24 kHz with constant wave cycle were used. Milk was treated for 2.5, 5, 7.5 and 10 min with sonification at 20 °C (room temperature) and thermosonification (ultrasound at temperature higher than room temperature) at 55 °C. The purpose of this study is to investigate the effect of high-power ultrasound combined with a slightly increased temperature on whole, skimmed and skimmed cow’s milk pretreated with bactofugation. Results and conclusions. The best sensory quality was achieved when milk was treated with ultrasound power of 200 W at 20 °C for max. 7.5 min. This research shows the potential of the applications of high-power ultrasound in dairy industry combined with bactofugation as a pre-treatment of milk at a slightly increased temperature (up to 55 °C). Novelty and scientific contribution. The application of these two treatments requires milder processing conditions than pasteurization, it is economical and more environmentally friendly technological process that preserves better nutritional values of milk, which is preferred by consumers., Pozadina istraživanja. Primjenjene su dvije metode obrade mlijeka: ultrazvuk (inovativna metoda) i baktofugiranje, nakon čega su ispitana fizikalno-kemijska i senzorska svojstva mlijeka, s osnovnom svrhom postizanja kakvoće i konzistencije pasteriziranog mlijeka. Eksperimentalni pristup. Korištena je snaga ultrazvuka od 200 i 400 W pri frekvenciji od 24 kHz s konstantnim valnim ciklusom. Mlijeko je tretirano sonifikacijom tijekom 2,5; 5; 7,5 i 10 min na 20 °C (sobnoj temperaturi) i termosonifikacijom (primjenom ultrazvuka na temperaturi višoj od sobne temperature) na 55 °C. Svrha je ove studije bila istražiti učinak ultrazvuka velike snage u kombinaciji s djelomično povišenom temperaturom na sirovo punomasno, obrano i obrano kravlje mlijeko prethodno obrađeno baktofugiranjem. Rezultati i zaključci. Najbolja senzorska kakvoća postignuta je obradom mlijeka ultrazvukom snage od 200 W pri 20 °C, tijekom maksimalno 7,5 min. Ovo istraživanje pokazuje potencijal primjene ultrazvuka velike snage u mljekarskoj industriji u kombinaciji s baktofugiranjem kao postupkom prethodne obrade mlijeka na djelomično povišenoj temperaturi (do 55 °C). Novina i znanstveni doprinos. Tijekom primjene ova dva postupka prerade mlijeka koriste se blaži uvjeti obrade od pasterizacije, pa se mogu smatrati ekonomičnim i ekološki prihvatljivijim tehnološkim postupcima, pomoću kojih se može bolje očuvati hranjiva vrijednost mlijeka, a što preferiraju i potrošači.

Ultrasonication is a non-thermal method of food preservation that has the advantage of inactivating microbes in food without causing the common side-effects associated with conventional heat treatments, such as nutrient and flavour loss. In this work high intensity ultrasound was used to investigate inactivation Enterobacteriae count in raw milk. Raw milk with 4% of milk fat was treated with ultrasonic probe that was 12 mm in diameter and with 20 kHz frequency immerged in milk directly. For ultrasounds treatment, three parameters varied according to the statistical experimental design. Centre composite design was used to optimize and design experimental parameters: temperature (20, 40 and 60 °C), amplitude (120, 90 and 60 μm) and time (6, 9 and 12 minutes). All analyses were performed immediately after sonication and after 3 and 5 days of storage in refrigeration at 4 °C. The facts that substantially affect the inactivation of microorganisms using ultrasound are the amplitude of the ultrasonic waves, the exposure/contact time with the microorganisms, and the temperature of treatment. The achieved results indicate significant inactivation of microorganisms under longer period of treatments with ultrasonic probe particularly in combination with higher temperature and amplitude. Output optimal value of Enterobacteriae count has been defined by Statgraphics where lowest Enterobacteriae count (1.06151 log CFU mL-1) was as follows for specific ultrasound parameters: amplitude of 120 μm, treatment time for 12 min and temperature of 60 °C., Ultrazvuk kao netermalna metoda procesiranja hrane ima svoje prednosti pri inaktivaciji mikroorganizama u hrani u odnosu na klasične metode procesiranja hrane budući da uzrokuje manje negativnih učinaka npr. gubitak važnih nutrijenata te aroma. U ovom radu ispitivana je inaktivacija Enterobakterija u mlijeku primjenom ultrazvuka visokog intenziteta. Sirovo mlijeko sadržaja masti 4 %, tretirano je ultrazvučnom sondom promjera 12 mm i frekvencije 20 kHz. Eksperiment je planiran i proveden koristeći kompjuterski program STATGRAFICS (Centre composite design - CCD). Ultrazvučna obrada provedena je prateći tri parametra - temperaturu (20, 40 i 60 °C), amplitudu (120, 90 i 60 μm) te vrijeme procesiranja (6, 9 i 12 minuta). Sve analize provedene su neposredno nakon sonificiranja te nakon 3 odnosno 5 dana skladištenja uzoraka u hladnjaku na temperaturi od 4 °C. Inaktivirajući učinak ultrazvuka na mikroorganizme (Enterobakterije) ovisio je o primijenjenoj amplitudi ultrazvuka, vremenu i temperaturi procesiranja mlijeka. Dobiveni rezultati pokazuju značajan inaktivirajući učinak ultrazvuka kod dužeg perioda obrade ultrazvučnom sondom u kombinaciji sa povišenom temperaturom i amplitudom od 120 μm. Optimalna vrijednost (najmanja) Enterobakterija (1,06151 log cfu mL-1) u mlijeku određena je Statgraphics-om pri sljedećim uvjetima obrade ultrazvukom: amplituda 120 μm, vrijeme obrade 12 minuta i temperatura od 60 °C.

Svrha ovog rada je ispitati utjecaj tretiranja visokim hidrostatskim tlakom na reološka i termofizička svojstva modelnih sustava β-laktoglobulina i karagenana. Suspenzije β-laktoglobulina tretirane su visokim hidrostatskim tlakom od 300 do 600 MPa. Vrijeme tretiranja bilo je 5 i 10 minuta. Mjerenja reoloških svojstava modelnih sustava karagenana i β-laktoglobulina provedena su rotacionim reometrom, Rheometric Scientific RM-180 (Rheometric Scientific, Inc., Piscataway, USA), na temperaturi od 20 ºC. Reološki parametri određeni su upotrebom Ostwald de Waele-ovog zakona. Rezultati ispitivanja pokazuju da su svi ispitivani sustavi imali ne-newtonski, pseudoplastični karakter, te da uzorci tretirani visokim hidrostatskim tlakom imaju promijenjene reološke značajke uslijed djelomične denaturacije proteina proporcionalne primijenjenom tlaku i vremenu tretiranja. Temperature faznih promjena određene su metodom diferencijalne termičke analize (DTA). Utvrđeno je da visoki hidrostatski tlak značajno snižava temperaturu zamrzavanja i odmrzavanja modelnih sustava β-laktoglobulina, te da karagenan posjeduje određena krioprotektorska svojstva., The aim of this paper is to examine the influence of high hydrostatic pressure treatment on the rheological and thermophisical properties of β-lactoglobulin and carragenan model systems. Suspensions of β-lactoglobulin were treated with a high hydrostatic pressure in a range of 300 to 600 MPa. Holding period was 5 and 10 minutes. Measurements were performed using rotational viscosimeter Rheometric Scientific RM-180 at 20 oC. The rheological parameters were determined by the Ostwald de Waele law. The results of the investigation have shown that all investigated systems are non-Newtonian – pseudoplastic. All samples treated with high hydrostatic pressure have changed rheological characteristics. The extent of protein denaturation was proportional to the intensity of applied pressure and holding time. The phase transition temperatures were determined by differential thermal analysis (DTA). High pressure treatment caused depression of freezing point and melting point, respectively. Carragenan acts as a crioprotectant.