Browsing by discipline "Livsmedelsteknologi"

High pressure processing (HPP) is a cold pasteurisation method, in which the products are generally processed at 300–800 MPa for a few minutes. Processing generally happens below 45 °C, so the treatment preserves the nutritional and sensory properties of the products. The literature review discussed high pressure processing as a food processing method and studied its effects on food. The focus was on the effects on microbes, enzymes, structure and chemical properties of dairy and vegetable products. The aim of the experimental research was to study the effects of high pressure processing on the microbiological and sensorial shelf life of blueberry puree, raw milk and roasted cheese. The objective was also to examine the shelf life of the products that can be achieved when using high pressure processing. Blueberry puree was analyzed for microbiological quality, pH, color and sensory properties during storage of 2 months. Raw milk and roasted cheese was analyzed for microbiological and sensory quality. Roasted cheese was also analyzed for total solids content. The raw milk was stored for 1 month and the roasted cheese for 3 months. The microbiological quality of high pressure processed raw milk remained good about two weeks. The sensory quality remained good for about 9 days. After three weeks, the high pressure processed raw milk reached the same microbiological level than reference sample on day 1. No difference occurred in color and pH between the high pressure processed blueberry puree samples and the reference samples during the storage. High pressure processed blueberry puree remained microbiologically high quality 8 weeks, while the reference puree was good only for 2 weeks. All blueberry purees remained sensorically good for 8 weeks. The shelf life of the roasted cheese after high pressure processing was approximately 1 month: reference samples remained good for 2 weeks. Mini roasted cheese remained microbiologically good for up to 3 months while the sensory quality declined after 2 months. High pressure processing significantly increases the microbiological shelf life of the product. Enterobacteriaceae, yeasts and molds are effectively inactivated by high pressure processing. Pseudomonas bacteria, which can produce pressure resistant enzymes like lipases, are more resistant to high pressure.

Tutkimuksen tavoitteena oli selvittää kuorittavuuteen vaikuttavia tekijöitä kuorettoman nakin valmistusprosessissa. Kirjallisuusosa käsitteli kuorittavuuteen vaikuttavia tekijöitä yleensä. Kokeellisen osan tavoitteena oli tutkia joidenkin massan ominaisuuksien vaikutusta kuorittavuuteen. Lisäksi työssä kehitettiin menetelmä kuorittavuuden mittaamiselle Instron-aineenkoestuslaitteella. Kuoreton nakki valmistetaan siten, että massa ruiskutetaan selluloosakuoreen, joka savustuksen, kypsennyksen ja jäähdytyksen jälkeen kuoritaan nakin päältä pois ennen pakkaamista. Erilaiset kuorintaongelmat, jotka hidastavat muuten tehokasta valmistusprosessia, ovat tavallisia. Kirjallisuuden mukaan kuorittavuutta helpottaa nakin sileä pinta. Sileän pinnan muodostumiseen on todettu vaikuttavan olosuhteet (lämpötila, suhteellinen kosteus, aika) savustamisen, kypsennyksen ja jäähdytyksen aikana. Myös joillakin raaka-aineilla, kuten sidekudoksella ja sokereilla, sekä raaka-aineiden ominaisuuksilla (lihan rasvan määrä ja laatu) on todettu olevan vaikutusta kuorittavuuteen. Tutkimuksessa kehitetty mittausmenetelmä selluloosakuoreen ruiskutetun nakin kuorittavuudelle perustui Instron-aineenkoestuslaitteella mitattavaan kuorintavastukseen. Kuorimaton nakki kiinnitettiin laitteen pidikkeeseen ja kuoren päät kiinnitettiin yläpuolella olleeseen toiseen pidikkeeseen. Laite veti pidikkeitä erilleen 10 cm matkan nopeudella 10 cm/min. Laite veti kuorta nakin päältä pois ja mittasi samalla vastustavan voiman (N). Mittauksen maksimiarvo kuvasi kuorimiseen tarvittavaa voimaa. Yhdestä näytteestä suoritettiin vähintään 5 rinnakkaista mittausta, joiden maksimiarvojen keskiarvoa käytettiin näytteen kuorittavuutta kuvaavana tunnuslukuna. Mittaustulokset olivat samansuuntaisia kuin havainnot tuotanto-olosuhteissa suoritetussa koekuorinnassa samoilla näytteillä. Vaikuttaa siltä, että kehitetyn mittausmenetelmän antamia tuloksia voidaan käyttää arvioitaessa kuorittavuutta tuotanto-olosuhteissa.

The cold storage, utilized to increase the shelf life of raw milk, favors the growth of psychrotrophic bacteria. Psychrotrophs are considered as problematic because they produce heat-stable spoilage enzymes. In addition, some pathogenic bacteria are capable of growing at cold storage temperatures and it has been observed in previous studies that the psychrotrophs in raw milk can be resistant to several antibiotics. In the literature review section of this study, the microbial composition of raw milk and the effect of cold storage, nitrogen gas (N2) treatment and activation of the lactoperoxidase system (LPS) on the raw milk bacteria was reviewed; moreover, the evolution, spread and mechanisms of bacterial antibiotic resistance and the antibiotic resistance on dairy farms and of raw milk bacteria was reviewed. Also the methods to study raw milk bacteria and their antibiotic resistance were documented. The aim of the experimental part was to study the effects of cold storage, N2 gas treatment and LPS treatment on the levels of antibiotic resistant bacteria in raw milk. Untreated, N2-treated and LPS-treated raw milk samples were stored at 6 °C and the counts of bacteria resistant to gentamicin, ceftatzidime, levofloxacin and trimethoprim-sulfamethoxazole were determined in the beginning of the experiments and after three and seven days of cold storage. The antibiotic resistance and spoilage features of bacterial isolates selected from different plates were compared. In addition, DNA fingerprints of selected isolates were obtained by rep-PCR method and for a couple of isolates 16S rRNA gene partial sequencing was performed. The presence of certain antibiotic resistance genes for the isolates partially identified was investigated using a PCR-based method. The length of cold storage affected the proportions of antibiotic resistant bacteria in raw milk. The proportions of antibiotic resistant bacteria in the control milk sample were generally, with the exception of TS-resistant bacteria in some cases, at their lowest after seven days of cold storage when the milk was, though, microbiologically unacceptable. There was a lot of variation in the prevalence of bacterial antibiotic resistance between the milk samples treated differently. The proportions of resistant bacteria were on average clearly higher in LPS samples than in control samples, whereas the effect of the N2 treatment on the proportions of resistant bacteria varied between the experiments. The bacterial isolates resistant to all the considered antibiotics produced less frequently protease and phospholipase than the isolates resistant to fewer antibiotics. The isolates from LPS samples were more frequently resistant to all the antibiotics studied and produced less frequently protease and phospholipase than the isolates from control and N2-treated samples. On the basis of the rep-PCR fingerprints, there were both similar and different strains among the bacterial isolates. Based on the 16S rRNA partial gene sequence, two isolates were identified as Pseudomonas spp. and two isolates as Stenotrophomonas spp. The targeted antibiotic resistance genes were not detected among the considered isolates. Possible reasons can be variations in the gene sequences, suboptimal PCR conditions or that the isolates lacked the genes studied. A PCR product was obtained for one Pseudomonas isolate using mexA-F/R primers, but according to the database the gene sequence did not show homology with antibiotic resistance genes. Further analyses would be required to confirm if the gene studied is linked to antibiotic resistance.

Lactic acid bacteria Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus are used for yoghurt manufacture. Traditional Northern fermented milk products are typically made with mesophilic species. In traditional Finnish product, viili, also secondary culture of Geotrichum candidum is used. In Finland during last 20 years, the consumption of yoghurt is doubled while the consumption of viili has dropped by half. The aim of this study was to continue the research for designing a novel fermented milk product ”termoviili”. The aim is to develop a product that combines the main flavour compound of yoghurt, acetaldehyde, to Geotrichum candidum. There were 12 LAB strains in this study. Their ability to grow in UHT-milk and produce acetaldehyde was studied. The acetaldehyde level, microbial growth and final pH were measured. Also strain identifications were done by using PCR-methods. All the LAB strains studied were able to grow at target temperature (+ 30°C). The amount of acetaldehyde produced varied between 0−22,5 mg acetaldehyde / 1 litre product. The main problem with all the LAB strains studied was their poor ability to decrease the pH of the milk fast enough and without any supplements. Growth supplement (sodium formate) and the addition of G. candidum were found to speed up the decrease of pH in some cases. The best strain to produce acetaldehyde was isolated from a commercial product and it was confirmed as Lactobacillus delbrueckii. According to Cheng (2010) good flavoured yoghurt results when 23−40 mg/kg and at least 8−10 mg/kg of acetaldehyde are produced. Based on this evaluation, the amount of acetaldehyde found in this study, is sufficient to produce enough yoghurt aroma to the final product. More study need to be done to speed up the decrease of pH and to optimize the recipe. Also different strains of G. candidum should be tested for the possibility to increase the incubation temperature.

Milk production in Finland has changed during the latest decades. There are significant changes in cattle breeding, cattle feeding, milk collecting and transportation. Also processing of milk products has been developed. In addition, milk products are consumed in a different way than before. For example the consumption of fat-free milk and cheeses has increased whereas overall consumption of milk has decreased. In this master’s thesis milk products of DIPP (Diabetes Prediction And Prevention) nutrition study were classified based on their homogenization and heat-treatment. Creating the classification, the effects of heat-treatment or homogenization on milk proteins and fat globules were considered. The classification was done using information provided by literature and by major dairy manufacturers. Milk products were classified in one of the following groups based on the homogenization information: homogenized, non-homogenized, fat-free; and in one of the following groups based on the heat-treatment information: normally pasteurized or milder heat treatment, high pasteurized at < 100°C, high pasteurized or sterilized at ≥100°C. Milk consumption of children at the age of 6 months (n=1305), 1 year (n=1513) and 3 years (n=1326) was observed using both the updated classical DIPP - milk product classification and the newly created processing based classifications. It was observed that children used a lot of strongly heated milk-based products especially during their first year. At the age of six months mostly high pasteurized or sterilized at ≥100°C and homogenized milk products were used. Background variables such as breastfeeding, mother’s education and children’s living area (Pohjois-Pohjanmaa/ Pirkanmaa) were associated with milk product consumption both when using classical and process based classifications. This study introduces new information about children’s milk product consumption. The process based classification can also be used later when observing whether consumption of some specific kind of milk products can lead to appearance of type 1 diabetes.

The literature review of this thesis deals with light, conventional light sources and the effects of light on the quality of foods. Impacts of light on the quality of frozen foods were also discussed. Effects of fluorescent light on frozen food have been previously reported in the literature, but effects of LED light have not. The literature review also deals with the quality changes of foods caused by freezing and frozen storage. The significance of package during frozen storage was reviewed. The aim of the experimental study was to investigate whether there are differences between the effects on frozen food when exposed to fluorescent or LED light. Frozen strawberries, shrimps, lamb loins and ice cream were exposed to fluorescent and LED light for 4 weeks. The samples were packed in transparent LDPE pouches except the lamb loins, which were vacuum-packed in transparent PA/PE film. References were packed in aluminium foil. Temperature of the samples was monitored by the sensors attached to the surfaces of the packages. The colour of the samples was measured every week using a spectrophotometer. Thiobarbituric acid (TBA) values of the shrimps and lamb loins were analysed after 0, 2 and 4 weeks of exposure. The odour of shrimps was evaluated with sensory evaluation using a multiple comparison test. Sensory evaluations of ice cream was conducted by trained panelists using a multiple comparison test. All the sensory evaluations were conducted after 2 and 4 weeks of exposure. In addition, ice cream was exposed to light under a yellow plastic film to find out the effects of riboflavin, which is known to operate as a sensitiser. After 4 weeks of exposure to the fluorescent light the total colour difference of the samples was higher than that of the products exposed to the LED light. Differences were pronounced especially in ice cream exposed to light under transparent film. The smell and taste of ice cream were affected when exposed to light under transparent or yellow plastic films. There were no statistically significant differences in the taste of ice cream when exposed to fluorescent or LED light for 4 weeks, but the smell of ice cream appeared to be more divergent from the reference when exposed to LED light under transparent film for 4 weeks than the smell of ice cream exposed to fluorescent light for 4 weeks. On the basis of this study, fluorescent light affected the colour of the frozen food more than LED light. Light sources did not differ from each other, when the results of the sensory evaluation of shrimps were considered. Because TBA values of lamb loins and shrimps also increased in reference samples, the effects of light could not be separated. Sensory properties of ice cream were affected by light exposures, but on the basis of sensory evaluation it is not possible to state which light source was more detrimental to the quality of ice cream.

Raakamaidon kylmäsäilytys suosii psykrotrofisten pilaajabakteerien kasvua. Raakamaidosta eristetyillä psykrotrofisilla pilaajabakteereilla on havaittu olevan sekä antibioottiresistenssi- että hemolyysiominaisuuksia. Tutkielman kirjallisuuskatsauksessa käsiteltiin raakamaidon mikrobistoa ja psykrotrofisia bakteereja. Kirjallisuuskatsauksessa tarkasteltiin myös bakteerien antibioottiresistenssiä, antibioottiresistenssin mekanismeja, antibioottiresistenssin leviämistä elintarvikeketjun välityksellä, lehmän raakamaidon bakteerien antibioottiresistenssiä ja bakteerien hemolyyttisiä ominaisuuksia. Kirjallisuuskatsauksessa käsiteltiin lisäksi raakamaidon bakteerien antibioottiresistenssin määrittämistä ja Pseudomonas-suvun bakteerien tunnistamista eri tutkimusmenetelmillä. Kokeellisen osuuden tavoitteena oli tutkia lehmän raakamaidosta eristettyjen psykrotrofisten bakteeri-isolaattien hemolyyttisiä ominaisuuksia kahdella menetelmällä: verimaljaviljelyllä ja WLA-testillä. Tarkoituksena oli tutkia myös isolaattien antibioottiresistenssiä ATB VET-testillä sekä määrittää isolaattien antibioottiherkkyyttä (MIC-arvot) Etest-, HiComb- ja Biolog PM12-testeillä. Tämän lisäksi tavoitteena oli tutkia isolaattien genomien sormenjälkiä rep-PCR-analyysin perusteella ja tunnistaa tutkitut isolaatit rpoB-geenianalyysin perusteella. Lähes puolet tutkituista raakamaidosta eristetyistä psykrotrofisista bakteeri-isolaateista (30) olivat hemolyyttisiä. Viisi isolaattia reagoivat WLA-testissä positiivisesti. Seitsemän isolaattia olivat multiresistenttejä antibiooteille ATB VET-testien perusteella. Kuitenkin suurin osa isolaateista olivat herkkiä levofloksasiinille ja gentamysiinille, mutta kohtalaisen resistenttejä kefotaksiimille ja trimetopriimi-sulfametoksatsolille MIC-määritysten perusteella. MIC-määritysten tulosten luotettavuuden varmistamiseksi tulisi tehdä rinnakkaismäärityksiä samalla menetelmällä. Kaksi tutkittua isolaattia olivat resistenttejä lähes kaikille tutkituille antibiooteille Biolog-testien perusteella. Rep-PCR-analyysin perusteella isolaatit olivat geneettisesti hyvin monimuotoisia ja isolaattien joukossa oli useita bakteerityyppejä. Suurin osa isolaateista tunnistettiin Pseudomonas fluorescens-bakteerilajiksi analysoidun rpoB-geenisekvenssin perusteella. Yksi isolaateista tunnistettiin Pseudomonas fluorescens- tai Pseudomonas trivialis-lajiksi. Yksi isolaatti tunnistettiin patogeeniseksi Stenotrophomonas maltophilia-lajiksi. Tulosten perusteella rpoB-geenin sekvensointi soveltui hyvin Pseudomonas-suvun bakteerien tunnistamiseen lajitasolla.

The literature review dealed with the extrusion processing, producing protein-rich extrudates, the attributes of extrudates and the future of snack-foods produced by extrusion cooking. The aim of the experimental study was to examine the influences of broiler meat and extrusion parameters to the structure of extrudates. The following variables were used: meat content of processed flour mixture, water content of processed dough and temperature of the sixth section and the die. Response variables were hardness of extrudates, expansion index (SEI) of extrudates, water content of extrudates, torque of the extruder’s screws and pressure of the extrusion dough at the die. The CCF modified Box-Behnken’s experimental design was used with total of 21 experiments. The meat content of the processed flour mixture was 10, 20 or 30%, the water content of the processed dough was 16, 18 or 20% and the processing temperature of the sixth section and the die was 110, 130 or 150 °C. Screw speed was 400 rpm and the feed rate was 68 g/min. The results were analyzed by Partial least squares regression (PLSR) and by Multiple linear regression (MLR) analysis with Matlab R2017b software. The sensory attributes of the extrudates were also observed. Regression analysis showed that torque of the screws was statistically significantly lower when the meat content of the processed flour mixture increased. Pressure at the die was statistically significantly lower when the water content of the dough, the temperature of the sixth section and the die or the meat content of the processed flour mixture increased. The water content of the extrudates was statistically significantly higher when the temperature of the sixth section and the die or the water content of the processed dough increased. The hardness of the extrudates was statistically significantly higher and the expansion index of the extrudates was statistically significantly smaller when the meat content of the processed flour mixture increased. Extrudates containing broiler meat were successfully prepared using extrusion cooking and differences of changing process parameters on structure of extrudates were detected.

Kauran ja ohran (1→3)(1→4)-β-D-beetaglukaanit muodostavat viskooseja liuoksia ja kykenevät muodostamaan geelejä. Geeliytymisominaisuuksiin vaikuttavat molekyylin rakenne (kuten sellotriosyyli- ja sellotetrasyyli yksiköiden–suhde), koko, beetaglukaanin pitoisuus liuoksessa ja varastointiaika. Kirjallisuuskatsauksessa käytiin läpi beetaglukaanin viskositeetin ja geeliytymisen merkitystä elintarviketeollisuuden tarpeille sekä terveysvaikutuksille. Lisäksi käytiin läpi tekijöitä, jotka vaikuttavat viskositeettiin ja geeliytymiseen. Työn tavoitteena oli selvittää, miten liukenemislämpötila ohjaa ohran ja kauran beetaglukaanin viskositeettia ja geeliytymistä, kun pitoisuus on pieni (ohra 1 % ja kaura 1,5 %). Lisäksi tarkasteltiin, miten liuoksen hapettaminen vaikutti geeliytymiseen. Beetaglukaania liuotettiin 37, 57 ja 85 ºC:een lämpötiloissa ja sen jälkeen puolet näytteistä hapetettiin 70 mM vetyperoksidilla. Näytteiden viskositeettia ja geeliytymistä mitattiin päivinä 1, 4 ja 7 näytteen valmistamisen jälkeen reometrillä ja lisäksi näytteiden sameutta tutkittiin spektrofotometrillä samoina päivinä. Geeliytymislämpötilan optimoimiseksi kauran betaglukaanille tehtiin vielä lisätestejä 35, 37, 40, 45 ja 50 ºC:ssa. Beetaglukaani liukeni 85 ºC:ssa veteen lähes täysin muodostaen jonkin verran viskooseja liuoksia. Hapettuneiden näytteiden viskositeetit laskivat varastoinnin aikana. Nämä liuokset eivät geeliytyneet varastoinnin aikana. Ohran beetaglukaaneista 57 ºC:ssa liuotettu oli viskoosein, ja kauran beetaglukaaneista 37 ºC:ssa liuotettu oli viskoosein. Ohran beetaglukaani kykeni muodostamaan geeliä ainoastaan, kun se oli liuotettu 57 ºC:ssa, kun taas kauran beetaglukaanilla oli laajempi liuotuslämpötila alue. 37 – 50 ºC:ssa liuenneet kauran beetaglukaanit muodostivat geelin. Hapettamattomien näytteiden muodostamat geelit olivat vahvempia kuin hapetettujen. Tulosten perusteella liuotuslämpötilalla oli suuri vaikutus sekä kauran että ohran beetaglukaanin viskositeettiin ja geeliytymiseen. Optimaalinen liuotuslämpötila viskositeetin ja geeliytymisen kannalta ohran beetaglukaanille oli 57 ºC ja kauran beetaglukaanille 37 – 45 º.

Tutkielman kirjallisuusosuudessa paneuduttiin kauran makromolekyyleihin ja niiden toiminnallisuuteen ja reologisiin mittausmenetelmiin sekä hydrolysoiviin entsyymeihin. Lisäksi kirjallisuusosuudessa perehdyttiin emulsio- ja vaahtorakenteisiin sekä hydrokolloideihin ja niiden merkitykseen elintarvikerakenteissa. Kokeellisen osan tavoitteena oli muodostaa kylmäsäilytyksen kestävä täysjyväkaurapohjainen lusikoitava emulsiorakenne. Lisäksi tavoitteena oli selvittää voiko täysjyväkauraemulsion makeuttaa luonnollisesti ja muuttaako makeuttaminen emulsion rakennetta ja sen pysyvyyttä. Työssä käytettiin täysjyväkauraa kaurafraktioiden sijaan, jolloin sivuvirtoja ei muodostunut ja prosessointiin käytettävä energia pysyi minimissään. Lisäksi emulsio sisälsi kaikki tunnetut täysjyväkauran ravitsemusta ja terveyttä edistävät tekijät ja toiminnalliset ominaisuudet. Makeus luotiin entsymaattisen hydrolyysin avulla. Emulsion mekaanista pysyvyyttä vahvistettiin hydrokolloidilla ja mikrobiologista säilyvyyttä parannettiin hapon lisäyksellä. Emulsion pysyvyyttä seurattiin kolmen viikon kylmäsäilytyksen aikana aistinvaraisella arvioinnilla ja mittaamalla viskositeettia, pisarakokojakaumaa ja synereesin määrää. Kirjallisuustiedon perusteella kauran lämpökäsittelyn arveltiin heikentävän emulsion rakennetta ja sen pysyvyyttä, mutta tätä ei havaittu tutkimuksessa. Täysjyväkauran tärkkelyksen liisteröinnin ja emulgoinnin avulla täysjyväkauraseoksesta saatiin aikaan miellyttävä lusikoitava emulsiorakenne, jonka pysyvyys parani luontaisen hydrokolloidin lisäyksellä ja happaman pH:n ansiosta. Entsymaattisen hydrolysoinnin ansiosta kauraseos makeutui ja emulsion täysjyväkaurapitoisuutta voitiin suurentaa lähes kaksinkertaiseksi verrattuna entsyymikäsittelemättömään emulsioon. Tässä työssä tutkitulla prosessilla voidaan lisätä välipalatuotteen täysjyväkaurapitoisuutta, joka parantaa välipalatuotteen ravitsemuksellisia ja terveydellisiä etuja.