Studies of the Effects of Industrial Processing on Fruit

Research output: ThesisDoctoral Thesis (compilation)


The industrial production of preserves includes several unit operations which all affects sensorial properties as well as the nutritional value of the final product. Thawing is a crucial unit operation, since then both chemical and physical changes take place.

Thawing strawberries in selected aqueous media could gave both firmer strawberries and smaller weight loss than if air was used as the thawing medium.

Upon mixing with sugar solution juice will diffuse out of the strawberries and into the solution. At the same time, some solids will be taken up from the solution. A model for the final volume of the strawberries is presented. Also, the composition of the sugar will change due to the invertase activity in the strawberries. The inversion affects both the natural sucrose as well as that added. The extent of inversion depends on the shape of the strawberries and on the duration of the immersion. The reaction takes place inside or in contact with the strawberry tissue. The reaction is important since the composition of the sugar affect the essential qualities of the final jam product.

Fresh berries and fruits are considered to be good sources of antioxidants. The antioxidative capacity in strawberries was measured before freezing and after an accelerated storage 40 C for 7 days. The loss of antioxidative capacity was small and could be related to the reduction of ascorbic acid.

In a final study blackcurrant jam was stored for 13 months during which time changes in ascorbic acid, beta-carotene and anthocyanins were monitored. After storage at 8 C the jam could still be considered a good source of ascorbic acid. In jam stored at a higher temperature the content of ascorbic acid was lower. Also the amount of anthocyanins were negatively affected by an elevated storage temperature. The amount of beta-carotene did not change during storage.


  • Uno Viberg
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Food Engineering


  • Food and drink technology, antioxidants, invertase, thawing, blackcurrant, strawberry, fruit, berry, Livsmedelsteknik
Original languageEnglish
Awarding Institution
Supervisors/Assistant supervisor
  • [unknown], [unknown], Supervisor, External person
Award date1998 Apr 4
  • Food Engineering, Lund Univeristy
Publication statusPublished - 1998
Publication categoryResearch

Bibliographic note

Defence details Date: 1998-04-04 Time: 10:15 Place: Lecture hall C, Center for Chemistry and Chemical Engineering External reviewer(s) Name: Sereno, Alberto M.C. Title: Professor Affiliation: University of Porto, Porto, Portugal --- Article: Viberg, U. and Sjöholm, I. The use of iso-osmotic solutions, applied to the thawing ofstrawberries. (Submitted to: Journal of Food Engineering) Article: Viberg, U., Freuler, S., Gekas V. and Sjöholm, I. Osmotic pretreatment ofstrawberries and shrinkage effects. (In press in: Journal of Food Engineering) Article: Viberg, U. and Sjöholm, I. Sucrose inversion during osmotic pretreatment ofstrawberries. (Submitted to: Lebensmittel -Wissenschaft und Technologie) Article: Viberg, U., Alklint, C., Åkesson, B. and Sjöholm, I. Changes in antioxidant capacity,ascorbic acid and anthocyanins in strawberries during freezing, processing andaccelerated storage in the presence of copper and iron (Manuscript) Article: Viberg, U., Ekström, G., Fredlund, K., Öste, R.E. and Sjöholm, I. A study of someimportant vitamins and antioxidants in a blackcurrant jam with low sugar contentand without additives.Int. J. Food Sci. and Nutr., 48, 57-66. 1997.