Ingegerd Sjöholm

Effect of processing on major flavonoids in processed onions, green beans, and peas

The contents of flavonoids in onions, green beans, and peas have been analysed in relation to the effect of different heat treatments. Two major flavonoids were studied, quercetin and kaempferol. The identification and quantification of the flavonoids were performed with high performance liquid chromatography and UV detection. The greatest loss of flavonoids in onion took place during the pre-processing step where the onion was peeled, trimmed, and chopped before blanching. Blanched onion contained 25 mg quercetin and 0.35 mg kaempferol per 100 g edible part. Blanched green beans contained 1.3 mg quercetin and 0.24 mg kaempferol per 100 g, and blanched peas only 0.15 mg quercetin per 100 g. No kaempferol was detected in peas. Further cooking, frying or warm-holding for up to 2 h of the blanched vegetables, did not influence the flavonoid content. Onions in ready-made dishes and home-cooked food as well as green beans may be good dietary sources of flavonoids.

Apple shrinkage upon drying

Abstract In this paper results from a study of the shrinkage of Mutsu apple slices during drying in a connective oven are presented. The results are expressed as relationships between volume and thickness reduction as well as between volume reduction and water content. No differences were observed with respect to slice size. Volume change was correlated to thickness change through an exponent of 1.50±0.24 for all samples measured. Volume change was linearly correlated with water content with r = 0.95.

Osmotic dehydration of apples —effects of agitation and raw material characteristics

Abstract The effects of agitation and structural differences on osmotic dehydration were investigated. Osmotic dehydration was performed in an agitated vessel at 20 °C using a 50% sucrose solution as the osmotic medium. The impellers Reynolds number was used for agitation quantification. Samples were separated into inner and outer apple parenchymatic tissue, the intercellular space interconnectivity and aspect ratio (length to width ratio) being higher in inner than outer tissue. Structural differentiation revealed a strong effect on process responses. Solid gain (kg/kg i.m.) was higher in inner than in outer apple parenchymatic tissue independently of agitation level. Water loss (kg/kg i.m.) was lower in inner than outer apple parenchyma at the same Reynolds number. Water loss was higher in the turbulent flow region than in the laminar flow region. Thereby, external mass transfer limitations were verified for our experimental conditions. Solid gain did not show significant differences between laminar and turbulent flow regions. The data indicate that free convection is the mechanism used by the solution in pore penetration, although lack of understanding of this phenomenon at the cell level prevented conclusions from being drawn. Attempts to explain experimental variations revealed indications suggesting the influence of initial bulk density and initial water content on water loss and solid gain.

Mechanisms and prevention of plant tissue collapse during dehydration: a critical review.

Referee: Prof. dr hab. Piotr P. Lewicki, Department of Food Engineering and Process Management, Warsaw Agricultural University, U1. Nowoursynowska 159c, 02-787 Warszawa, Poland The appearance and functional properties are primordial in the quality assessment of semifinished fruit and vegetable products. These properties are often associated with shrunken, shriveled, darkened materials of poor rehydration ability after been subjected to air-drying — the most used drying method in the food industry. Fruits and vegetables are cellular tissues containing gas-filled pores that tend to collapse when subjected to dehydration. Collapse is an overall term that has different meanings and scale-settings in the literature depending on whether the author is a plant physiologist, a food technologist, a chemical engineer, or a material scientist. Some clarifications are given in this particular but wide field. The purpose of this work was to make a state-of-the-art contribution to the structural and textural effects of different types of dehydration on edible plant products and give a basis for preventing this phenomenon. The plant tissue is described, and the primordial role of the cell wall in keeping the structural integrity is emphasized. Water and its functionality at macro and micro levels of the cellular tissue are reviewed as well as its transport during dehydration. The effects of both dehydration and rehydration are described in detail, and the term “textural collapse” is proposed as an alternative to structural collapse.

Osmotic dehydration of apples. Shrinkage phenomena and the significance of initial structure on mass transfer rates

The existence of two well-defined structures in the parenchymatic tissue of apples (the flesh) gave us the opportunity to study the significance of the initial structure on mass transfer rates of two apple varieties, Kim (Sweden) and Granny Smith (Argentina) when subjected to osmotic dehydration. Our results verified the importance of the initial structure for osmotic processing responses. Knowledge of the properties of the tissue and the solution penetration into the intercellular space, permitting us to explain the kinetics found. Shrinkage properties such as volume changes, bulk density, particle density and porosity, have been studied macroscopically for both structures, inner (close to core) and outer (close to skin) and presented as a function of water content in a manner similar to air drying practice. A comparison with shrinkage properties observed in air drying is attempted.

Influence of packaging material and storage condition on the sensory quality of broccoli

The sensory quality of broccoli stored in modified atmosphere packages was studied. Oriented polypropylene (OPP), polyvinyl chloride (PVC) and low-density polyethylene (LDPE) were used as packaging ...

Plant Stress Physiology: Opportunities and Challenges for the Food Industry

We review and analyze the possible advantages and disadvantages of plant-stress-related metabolic and structural changes on applications in the fruit and vegetable processing industry. Knowledge of the cellular and tissue transformations that result from environmental conditions or industrial manipulation is a powerful means for food engineers to gain a better understanding of biological systems in order to avoid potential side effects. Our aim is to provide an overview of the understanding and implementation of physiological and biochemical principles in the industrial processing of fruits and vegetables.

Factors Affecting Quality and Postharvest Properties of Vegetables: Integration of Water Relations and Metabolism

Growing of vegetables in the field, harvesting, handling in the packing house and storage are events in the lifetime of vegetables that are analysed from the point of view of the complex series of physiological transitions taking place in each of these events. Water is the major factor limiting plant metabolism and plants have developed fascinating mechanisms to cope with this limiting factor. Therefore, water relations (water, pressure and osmotic potential) are used as criteria for discussing plant stress physiology aspects such as osmotic, elastic adjustment and cold acclimation, as well as mechanical stress when the vegetable is harvested and during handling in the packing house. Consequences for the storage potential and quality of the vegetable are discussed. After harvesting, the postharvest cell has the ability to complete a complex series of physiological transitions that will influence vegetable quality and further processing operations. Metabolic changes in the cytosol, cell membrane and cell wall are described.

Osmotic-treatment-induced cell death and osmotic processing kinetics of apples with characterised raw material properties

Three apple varieties cultivated in southern Sweden namely Jonagold, Kim and Mutsu were subjected to osmotic treatment at 5, 20 and 40 degreesC with a 50% sucrose solution. The evaluation of cell viability after osmotic processing, was carried out in Granny Smith apples from Argentina. The processing conditions were 50% sucrose solution at 20 degreesC and the viability assay used was based on the reduction of 2,3,5-triphenyltetrazolium chloride (TTC). The experimental samples were separated into inner (close to the apple core) and outer (close to the skin) specimens, due to the existence of pronounced structural differences between them. The kinetics revealed that for each apple variety and at each process temperature, samples of the outer structure exhibited higher water loss and lower solids gain than those of the inner structure. Overall, the Jonagold and Kim apples exhibited similarly high water loss, while Mutsu showed a lower loss. Jonagold absorbed the lowest amount of solids with Kim rating second and Mutsu apples showing the highest solids gain. The cell viability assay on the experimental samples revealed the first layer of cell in a depth 1-2 mm from the surface to die as a result of the severe osmotic shock

Effects of modified atmosphere on shelf-life of carrot juice

The effects of de-aeration and modification of the headspace atmosphere on carrot juice shelf-life were investigated. The shelf-life was defined by microbial growth, determined by isothermal calorimetry and plate counts. Compared with storage under air, de-aeration of carrot juice by helium or nitrogen bubbling, followed by flush packaging had no effects on shelf-life. Similar treatment with carbon dioxide, giving a carbonated drink, prolonged the shelf-life by up to 250%. This effect could not be explained by the change in pH to 5.6, since the shelf-life was not prolonged by the addition of hydrochloric acid until pH <4.5. Both the concentrations of H+ and of dissolved CO2 were correlated to the shelf-life of fresh carrot juice; higher concentrations giving shorter shelf-lives. The concentration of dissolved CO2 was also linearly correlated to the peak thermal power