Thylakoid membrane from spinach - effect of processing on their function as appetite suppressing ingredient

Abstract: Western diet contains a high proportion of palatable food, rich in refined carbohydrates and fat, that subsequently increases the risk of overconsumption and possibly leads to overweight and obesity. Therefore an approach to strengthen the inherent satiety for fat can be used to prevent overconsumption.
Thylakoid membranes isolated from the chloroplast of green leaves have been found to reduce the rate of lipolysis by inhibiting lipase/co-lipase. Administration of thylakoids to animals and humans reduced food intake and body weight as well as affected appetite-regulation hormones.
When a product for consumers shall be formulated based on a plant extract with appetite suppressing abilities, the material must maintain the functionality during industrial processing and storage. Heat treatment is often applied to assure the microbiological safety of the product, and to dry the plant extract into powder form increases the shelf life and flexibility in applications while at the same time also reduces transport and handling costs. The present thesis aims to investigate the effect of processing on thylakoids’ physicochemical properties and subsequent physiological functions of the appetite-suppressing ingredient.
Heat treatment reduced the ability to inhibit lipase/co-lipase in vitro. Heat treatment also affected chlorophyll content and the thylakoids’ ability to stabilize the oil-water interface in oil-in-water emulsions.
Drum drying, spray drying and freeze drying were investigated. Drying at higher temperatures decreased the emulsifying capacity of the thylakoids as well as reducing lipase-inhibiting effect. Deterioration processes was initiated during dehydration and continued during storage. Moisture in surrounding air had a definite effect on chlorophyll degradation with highest degradation rate in high relative humidity. Emulsifying capacity of thylakoid powders was impaired after storage and the reduction was accelerated at higher relative humidities. Spray-dried thylakoid powder had the highest chlorophyll content and the highest emulsifying capacity of all powders investigated. The mild heat treatment during dehydration preserved the chlorophyll content but was severe enough to partly inactivate degradation enzymes. Of the studied techniques, spray drying was concluded to be the most suitable drying technique with respect to functionality of the resulting powder after processing and storage.
A correlation between characteristics and functionality of the thylakoids was established both in aqueous solution and in powder formula. Chlorophyll content, green colour and lightness of powders and ability to stabilize the oil-water interface were correlated to lipase-inhibiting capacity. This opens possibilities to partly replace the enzymatic activity measurement method with the less time consuming and more cost efficient spectrophotometric method and emulsion-based model in screening processes, for example during process optimization.
In conclusion, the thesis contributes with knowledge about the effect of processing and storage on thylakoid products’ functionality. Thus the results can be applied in production of a more standardised functional food ingredient with optimized and predicted appetite reducing properties.