Sensory evaluation and instrumental methods were applied to the
evaluation of strawberry juice concentrate (68°Brix) stored at
20°C which had been produced both commercially (C-SJC) and in a
pilot plant (SJC). Sensory evaluation included taste and aroma
ratings by intensity scaling and time-intensity of taste, and visual
colorimetry by matching Munsell color chips. Instrumental analyses
included tristimulus colorimetry (i.e. Hunter colorimeter),
spectrophotometric colorimetry for pigment analyses, titrametric
analyses for acidity (pH and titratable acidity) and free α-amino
acids (formol number), and headspace gas analyses for CO₂ and O₂.
During six days storage of C-SJC, a decrease in concentration of
anthocyanins and increase in polyphenolics (tannin) was associated
with an increase in astringency. Free α-amino acids were
observed to decrease, while CO₂ was released. These changes were
associated with an increase in musty/moldy and pungent aromas. Free
sugars and titratable acidity did not change.
The pilot plant SJC was processed from blanched and unblanched
fruit to evaluate the relative importance of oxidase activity (i.e.
polyphenoloxidase) prior to pasteurization. The blanching treatment
increased the astringency and sourness in unstored SJC. These
affects were associated with an increase in concentration of
polyphenolics (tannin). During storage, the blanch treatment
decreased the rate of anthocyanin loss and decreased the release rate
of CO₂, yet degradation rates were still high. The 0₂
concentration in headspace did not change significantly during
storage indicating that polyphenoloxidase (PPO) activity during
storage was low. The musty/moldy and pungent aromas increased
similarly to C-SJC.
A chemical mechanism accounting for these changes is proposed
where products from the oxidative degradation of ascorbic acid
contribute directly or indirectly to the degradation of anthocyanins
to yield browning. Further, high initial concentrations and
subsequent decreases during C-SJC storage of free α-amino acids
indicate that Strecker degradation is a participating mechanism.
Associations of browning with the development of off-flavors suggest
this chemical mechanism forms odor-active volatile compounds. / Graduation date: 1989
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/27220 |
| Date | 27 January 1989 |
| Creators | Lundahl, David S. |
| Contributors | McDaniel, Mina R. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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