Browsing by Subject "colour"

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.

A common quality issue in fresh-cut vegetables is enzymatic browning. Anti-browning agents regulated by (EU) N:o 1129/2011 can be used in processing and vegetables are usually treated with compounds after washing and cutting. Polyphenol oxidase enzyme (PPO) in vegetables ox-idises phenolic compounds to quinones and brown melanin pigments are formed when reactive quinones polymerize. The literature review focused on phenolic compounds of apples, the mech-anism of action and inhibition of PPO. In addition, the review covered anti-browning agents in-vestigated in previous studies and physical inhibition methods for enzymatic browning. The aim of the experimental study was to find a mixture of anti-browning agents classified as a processing aid for fresh-cut apple with the help of the experimental design. In addition, apples treated with three different concentrations of calcium ascorbate were also investigated. The colour of the treated apples was measured using a colorimeter, the activity of PPO was determined spec-trophotometrically and the concentrations of the most common phenolic compounds of Granny Smith were determined by Ultra-High Performance Liquid Chromatography (UHPLC). The concentrations of anti-browning agents of the mixtures in PLSR model did not have a statis-tically significant effect on colour and the coefficient of determination was satisfactory. The ap-ples from the experimental design maintained their colour over one but less than five days and the apples treated with calcium ascorbate maintained their colour for one week which was the targeted shelf life. The PPO activity of the samples from the experimental design increased during the storage but activity of the samples treated with calcium ascorbate was zero all the time. The standard deviations of concentrations of phenolic compounds were high and no clear trend re-garding the change of concentrations and browning was noticed. The three major phenolic com-pounds of Granny Smith were (-)-epicatechin, (+)-catechin and chlorogenic acid. The concentra-tions of catechins were higher in the peel than in the flesh but for chlorogenic acid it was the opposite. The shelf life of one week was not achieved with the mixtures of the experimental design but calcium ascorbate acted effectively. Also compounds in the mixtures had the ability to inhibit the PPO because the apples did not start to brown immediately as the control samples treated with water. The results confirmed previous results from the literature that calcium ascorbate is an effective anti-browning agent and therefore it is one of the most common anti-browning agents in the fresh-cut industry.