CHEM215 Lecture 14: Lec 14 - Food Processing 3
Lecture 14 – Food Processing 3
Tea quality assessment 1 - tasting:
• Tea is exported to major distribution centres for quality assessment
• Tea tasters determines the quality/price of teas by studying various characteristics
and describing the with unique languages.
• Professional taster might taste and assess over 3000 teas a day.
• Tasting characteristics:
1. Colour —> an important characteristic of tea and determines flavour. Deep rich
red colour is desirable.
2. Astrigency —> drying sensation in the mouth
3. General mouthfeel
4. Tea cream formation —> as a tea cools, a precipitate is formed. This precipitate is a
mixture mainly of caffeine, theaflavins and thearubigans. Seeing this tea cream
formation is a good thing as it is an indicator of quality.
• Properties of tea cream
1. Precipitate is very difficult to re-dissolves
2. Colour varies depending upon composition. The colour of tea cream is a primary
quality indicator of TF/TR ratio. Bright orange/red colour indicates good quality as
more TF than TR. Yucky brown colour correlates to poorer quality and more TR
than TF.
The ratio of TF/TR depends on the duration of fermentation.
Tea quality assessment 2 - analytical chemistry:
All teas not also undergo chemical analysis for:
• Caffeine content
• Theaflavin content
• Thearubigan content
• Analytical techniques use:
-Caffeine: solvent extraction (separating caffeine from other molecules), then,
UV absorption spectroscopy. This enables us to generate a standard curve —>
generates linear curve based on Beer-Lamberts law. The higher the
caffeine content, the greater the absorbency
Or,
High performance liquid chromatography (HPLC). Measures absorbance versus
time, and allows us to develop a standard curve of area under the peak
versus concentration.
-Theaflavin/thearubigan content: extraction and complexation with Fe3+, then
UV absorption spectroscopy or HPLC.
(Need to make complexes of these molecules with Fe3+ before we are able
to measure them)
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Document Summary
Deep rich red colour is desirable: astrigency > drying sensation in the mouth, general mouthfeel, tea cream formation > as a tea cools, a precipitate is formed. This precipitate is a mixture mainly of caffeine, theaflavins and thearubigans. Seeing this tea cream formation is a good thing as it is an indicator of quality: properties of tea cream, precipitate is very difficult to re-dissolves, colour varies depending upon composition. The colour of tea cream is a primary quality indicator of tf/tr ratio. Bright orange/red colour indicates good quality as more tf than tr. Yucky brown colour correlates to poorer quality and more tr than tf. The ratio of tf/tr depends on the duration of fermentation. All teas not also undergo chemical analysis for: caffeine content, theaflavin content, thearubigan content, analytical techniques use: Caffeine: solvent extraction (separating caffeine from other molecules), then, This enables us to generate a standard curve > generates linear curve based on beer-lamberts law.
