Browsing by discipline "Food Technology"

Emulsified films are prepared by drying an emulsion. Polysaccharide based emulsified films consist of film-forming polysaccharide, fat, emulsifier and plasticiser. In the literature review, the materials used in the preparation of polysaccharide based emulsified films were discussed. The review also included a discussion of which factors affect the water barrier and mechanical properties of the emulsified films. The aim of the experimental study was to find out the potential of konjac glucomannan (KGM) and galactoglucomannan (GGM) in emulsified films. The effect of fat type and fat content on the water barrier and mechanical properties of the films were studied. Emulsified films which contained 30% (wt-% of GGM) fat were prepared from beeswax, rapeseed oil and pine wood oil. Fat contents of 10 and 50% were also used for beeswax. Emulsified films were compared with control films that did not contain any fat. The ratio of KGM and GGM used was 1:1. The water vapour permeability (WVP), water vapour transmission rate (WVTR), Young’s modulus, tensile strength and elongation at break were measured. Films were also viewed with a scanning electron microscope (SEM). KGM and GGM were suitable materials for emulsified films. The surfaces of films dried at room temperature were more uniform than those dried at 60 °C. In the SEM images, wax droplets were smaller than oil droplets. The diameter of oil droplets was about 10 ?m and 2–6 ?m for wax droplets. Wax droplets were better entrapped in the film matrix probably due to their smaller size. As expected, best water barrier properties were obtained with films containing 50% beeswax (p < 0.05). WVP of the films decreased when the content of beeswax in the film increased. Films containing 30% oils and 10% beeswax did not differ significantly from the control film in water barrier and in mechanical properties. The lowest Young’s modulus was with 50% beeswax film. The control film was the stiffest and strongest. There were no statistically significant differences in elongation at break between the films. Emulsified films were successfully prepared from KGM and GGM. The water barrier properties of emulsified films were better than those of the control film and still the mechanical properties were rather well maintained.

The fish processing industry requires a method by which shelf life of whitefish could be reliably assessed in real time. Quality Index Method (QIM®) has been used in several European countries for many different species of fish. QIM® predicts the remaining shelf life of fish species based on changes in sensory characteristics. The aim of the present study was to create the QIM® for sea-farmed whitefish, the first QIM® for Finnish fish, which could be included in the official QIM® folder. The study was conducted in the Finnish Food Safety Authorty (Evira). Examined fishes were purchased from Kalatukku E. Eriksson Ltd. pH value and a microbiological method were used to evaluate shelf life. Sensory profiles were created (n = 13). Two profile panels (n = 9) and the QIM® panel (n = 5) evaluated the raw and cooked fish. The result was also ensured by quality scoring for fish (Evira 8001). The QIM® panel created a draft for the QIM® frame, and the draft was further tested. Photos of fresh fish samples were taken. The QIM® draft created according to this study was an effective basis for initiating the validation of the QIM® prepared. It can also be noted that the QIM® itself was suitable for sea-farmed whitefish. Cooked fish analysed with a sensory evaluation method (Evira 8001), and found the time when you can find spoiled taste of from cooked fish and the examination of raw fish can be stopped. The microbiological method “Determination of the number of microbes” (Evira 3420/1) correlated with the QIM® result, fish samples were polluted on the fifteenth day. The pH results did not provide reliable results with which the QIM® result could have been compared. The prepared QIM® created for the sea-farmed whitefish could be utilised in the future in the Finnish fishing industry. It would be useful if QIM® was created for the other most common Finnish trade fish, so that the expiry dates on packages would be based on one common method, and thus the last day of use would have a scientific basis.

The literature review deals with sensory properties of apples, factors affecting consumer perception and apple acceptability and methods that can be used to study these phenomena. Apple cultivation and consumption in Finland and demands set by legislation were also examined. The aim of the experimental work was firstly to produce sensory profiles for eight domestic winter apple varieties (Amorosa, Aroma, Eva-Lotta, Konsta, Lobo, Red Atlas, Valtti and Åkerö Hassel), secondly to study consumers’ apple perception using a home-use-test and finally to use preference mapping to combine data from descriptive analysis and consumer test. Apples were evaluated at two different time points in order to study how ripening affects sensory properties and consumer perception. The panel in descriptive analysis consisted of 11 trained assessors. Participants of the consumer test (n=80) were mainly students and staff of the University of Helsinki. Eva-Lotta, Amorosa and Aroma had the sweetest flavour. Valtti and Red Atlas had the most acidic and astringent flavour with the highest flavour intensity. Lobo, Red Atlas and Konsta had the mealiest texture and ripening caused severe deterioration in texture for these three varieties. Aroma and Valtti had the crispiest texture while Lobo had the lowest texture crispiness. Eva-Lotta and Valtti were the juiciest varieties and had the highest scores in fruity aroma. Statistically significant differences between varieties were found in all other attributes except soggy texture and grassy aroma. Eva-Lotta was the most preferred variety. Eva-Lotta, Amorosa and Aroma had the most pleasant taste while Red Atlas and Åkerö Hassel had the least preferred taste. Strong correlation between overall liking and taste pleasantness was observed. Willingness-to-buy was mostly explained by overall liking. No explicit consumer groups were identified using cluster analysis which was probably due to homogeneity of the participants. Most of the participants preferred sweet and fruity apples although some exceptions were observed.

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.

The literature review was concerned with colourful vegetables and the most common pigments in vegetables: carotenoids, anthocyanins, betalaines and chlorophyll. In addition, how thermal treatments affect these pigments and the structure of vegetable was reviewed. The aim of the experimental work was to investigate the effect of thermal treatments on the colour, pigments and texture of carrots and beet-roots. Seven coloured carrot cultivars and four coloured beet-root cultivars were examined. Three different kinds of thermal treatments were applied to the samples: blanching, boiling and steaming. Orange and purple carrots contained the highest amounts of carotenoids. The total carotenoid content of the carrots increased due to the thermal treatments. Purple carrots were the only carrots which contained anthocyanins. Anthocyanin stability is pH dependent: boiling in slightly acidic water had a minor impact on anthocyanin content than boiling in pure water. Red beet was the most betalain-rich beet-root. Other cultivars contained remarkably less betalaines. Betalain content decreased due to the thermal treatments. Betalain degradation due to the thermal treatments was detected as the pigment content and colour changed. Thermal treatments softened the vegetable structure. Thermal treatment improves the extraction of the pigments from the vegetable structure, which was detected as the increase in pigment concentration, leading to an enhancement of bioavailability of pigments. However, long thermal treatments cause pigment degradation and reduce the nutritional value of the vegetables.

The literature review of this thesis deals with light, different light sources and their properties. LED (Light Emitting Diode) light was specially taken into consideration, because the use of LED lights will increase in general illumination. The literature review also deals with the quality changes of dairy products and potatoes caused by exposure to light. The aim of this study was to search for such a spectral distribution of light which would cause only minor changes in the sensory quality of milk and the surface colour of potatoes. Objective was to also find out if there is a difference between the effects of fluorescent light and LED light on the quality of milk and greening of potatoes. Reduced (1,5 %) fat milk and new potatoes were used as testing materials. The milk in commercial carton board packages was exposed to six different light sources: white fluorescent lamp, white LED and LED of four different colours. The potatoes packed in transparent LDPE (Low Density Poly Ethylene) bags were stored under five different light sources: white fluorescent lamp, white LED and LED of three different colours. The light intensity at the surface of the packages was about 1000 lx in both studies. In the milk study, the effects of light were evaluated with a sensory method using descriptive analysis. In the potato study, the light effects were analysed with colour measurements (avalue) using a spectrophotometer and with surface temperature measurements using a laser thermometer. Sensory evaluation of milk there resulted in few statistically significant differences in the intensity of the attributes between the milks stored under different light sources. Light exposure caused a rapid greening of potatoes in every illumination. According to colour change percentage, the greening order under different lights was: white LED < yellow LED < green LED < turquoise LED < fluorescent light. The potatoes which were stored in dark had no change in their surface colour. The surface temperature of potatoes increased most under white LED and turquoise LED lights. A spectral distribution of light which would have caused less changes in sensory quality of milk than commonly used fluorescent light was not found in this study. The results showed, however, that in addition to blue light which has always been considered the most harmful for milk the red light also caused remarkable quality changes. Based on the results of this study, it could be suggested that under the LED lights the quality of packed milk retained its quality characteristics at least as well as under the fluorescent light. There were differences between the effects of different lights on the greening of potatoes. White and yellow LED light caused less greening of potatoes than the other lights. The strongest greening of potatoes was observed under the fluorescent light.

In the literature section, knowledge was gathered about β-lactoglobulin, typical heat treatments and what effects they have on milk, sample preparation and the methods used in the practical part. Aim in the laboratory was to create a functional method for evaluating milk and whey samples using native-PAGE and Western blotting methods together with β-lactoglobulin specific antibody. The idea was to create a method able to tell apart and determine the most common treatment levels of milk from even tiny sample volumes. With the method developed in the practical study, it is possible to distinguish raw, pasteurized, ESL and UHT milks. Significant differences were found in the amounts of native and oligomer forms of β-lactoglobulin. The more intense the heat treatment, the less native forms are left on the gel, and there might not be any left in UHT milk. Number of small oligomers first increases from raw to ESL, but decreases again significantly in UHT milk. Almost all the protein in UHT milk is too large to enter the separation gel. Resolving power of the method seems excellent, since mere 2 µg BLG or 3 µl milk is enough to gain results even from thawed samples. In comparison to native-PAGE the antibody has better sensitivity and it gives BLG-specific information from smaller amounts than just the Native-PAGE method. However native-PAGE combined with Western Blotting is quite time consuming and prone to errors, and therefore this method is better suited to long term research purposes rather than daily routine monitoring of hear treatment.

Maisterintutkielman kirjallisuusosassa perehdyttiin tuorejuustoihin ja niiden valmistusmenetelmiin. Tässä tutkielmassa tutkittiin pääasiassa leikattavan tuorejuuston kolmea eri valmistusmenetelmää: säkitys-, ultrasuodatus- ja rahka-rasvaseosmenetelmää. Kirjallisuusosassa käsiteltiin lisäksi tuorejuustojen koostumusta, valmistusmenetelmien kannattavuutta, kuten tuorejuustosaantoa ja laatuominaisuuksia. Kokeellisessa osassa valmistettiin leikattavaa tuorejuustoa pilot-mittakaavassa ultrasuodatus- ja rahka-rasvaseosmenetelmällä ja verrattiin teollisesti säkitysmenetelmällä valmistettuun leikattavaan tuorejuustoon. Näytteistä tutkittiin valmistusmenetelmien vaikutuksia leikattavan tuorejuuston valmistusprosessiin, laatuun, rakenteeseen, aistinvaraisiin ominaisuuksiin, säilyvyyteen ja kannattavuuteen. Tuorejuustojen aistittavaa laatua tutkittiin perinteisen miellyttävyystestin avulla ja rakennetta erilaisin rakennemittauksin. Lisäksi juustoista määritettiin kemiallinen koostumus ja mikrobiologinen laatu. Eri valmistusmenetelmillä valmistetut leikattavat tuorejuustot erosivat toisistaan tilastollisesti merkitsevästi joiltakin rakenteellisilta ja aistinvaraisilta ominaisuuksiltaan. Yksi leikattava tuorejuustonäyte koettiin kokonaisuudessaan miellyttävimmäksi kaikilta arvioitavilta ominaisuuksiltaan. Lisäksi rakennemittausten tulokset tukivat hyvin kuluttajien aistinvaraisia arviointeja. Tuorejuustojen säilyvyyttä tutkittiin siten, että rakenne- ja mikrobiologisista määrityksistä tehtiin toistomittaukset viiden viikon kuluttua valmistuksesta. Toistomittauksien avulla voitiin tarkastella rakenteen ja mikrobiologisten tulosten muuttumista säilönnän aikana. Säilyvyys oli pysynyt hyvänä lukuun ottamatta säkitysmenetelmässä mikrobien pesäkemääriä, joiden tulosta vääristivät maitohappobakteerit.