Unit 3 Flashcards
What is the smell associated with Cis-3-hexane-1-ol =
cut grass
Flavors have 2 modes of formation:
Thermal and Enzymatic (including fermentation)
One way of classifying compounds is based on their mode of formation; flavors can be generated wither ____________ or by ___________ during food processing.
naturally
heat treatment
Natural flavors are mainly ______________________ (phytochemicals) of the living tissue, formed during the natural growth cycle of the organism by the action of enzymes, whereas flavors produced by heat treatment is the result of thermal _____________ and oxidation of various food ingredients and their complex interactions.
secondary metabolites
degradation
The initial or primary precursors of flavors are the polymers found in food such as ________, ________, _________ and DNA which can undergo either enzymatic or thermal hydrolysis, to produce the intermediate precursors mainly dimers and monomers
proteins
lipids
polysaccharides
The type of flavor effect depends on the conditions of ____________ and the type of the initial precursors found in the particular food product
processing
In terms of composition, thermally generated flavors are richer in ____________ compounds compared to enzymatically produced flavors
heterocyclic
What are the 3 groups of reactions that account for most chemical transformations of intermediate precursors in food:
- Maillard & Strecker reactions (caramelization)
- Thermal decomposition
- Lipid oxidation
Name the possible carcinogen in red raw meat:
N-glycolylneuraminic acid
The raw meat has no particular appealing flavor, however, during various processes of cooking, the initial precursors in meat, produce water soluble intermediate precursors, such as :
- glycopeptides
- free nucleotides
- peptides
- amino acids
- amino-sugars
- free sugars
- fatty acids
The meat flavor, therefore, is the combined effect of the chemicals produced from the _____________ of these intermediates and the products formed from the amino-carbonyl interactions, such as between the reducing sugars and amino acids this reaction is known as the Maillard reaction or ________________ since it is responsible also for the brown color produced when foods are heated
thermal degradation
non-enzymatic browning
__________ and __________ (dipeptides) are by far the most abundant amino compounds in red meat followed by sulfur containing amino acids (_____________ and ___________). Nucleotides and lipids can also undergo either enzymatic or thermal hydrolysis to produce nucleosides and free fatty acids as important intermediate precursors
Anserine and Carnosine
Cysteine and cystine
What are the intermediate precursors in meat:
- Amino acid/sugars
- Sulfur amino acids
- Fatty acids
- Thiamine & Ribose-5’-phosphate
Thiamin (vit B1) generates different _____________ at different pH values
volatile degradation products
Vitamin B1 structure can be classified has a ________________
heteroatom (sulfur, nitrogen + oxygen)
T or F: Thiamin produces hundreads of degradation products
T
T or F: Heterocyclic compounds have very low threshold values
T
T or F: Sugars caramelize at relatively high temperatures
T
If the sugar reacts with an amino acid then the temperature at which the sugar will degrade gets much _________
lower
What is the key aspect if we want to obtain beautiful browning reactions?
The key is of course dehydration, too much water will not generate browning (concentrated solution is best for that)
Fructose is what type of sugar?
Keto-sugar
Glucose is what type of sugar?
Aldehyde-suagr
When sugars are put in solution, they get into the ________________ and they are then able to receive amino acids
open-ring
Process of ring opening and closing is called:
tautomerization
T or F: Glucose is the least unstable sugar (open form = 0.005%), ribose has like 20% open-form and reacts even more with protein within our body which is unfavourable
T
Strecker aldehyde =
CH3CHO
What type of reaction involves an amino acid reacting with 2 carbonyls?
The Strecker reaction
During a strecker reaction we generate an _____________
aldehyde (called strecker aldehyde)
T or F: aldehyde is part of a group of aroma chemicals that are intensively aromatic (with very low threshold value) so its valuable for food industries to generate lots of aldehydes in food processing conditions such as strecker aldehydes
T
Acetaldehyde (CH3CHO) is the strecker aldehyde of _________
alanine
Formaldehyde (CH2O) is the strecker aldehyde of ____________
glycine
T or F: strecker aldehydes have special aroma properties
T
The first step involved in the processing of stimulant beverages, is fermentation and _____________ giving rise to flavor precursors. This step is followed by firing and drying in driers. In the case of coffee, another step of _______ (above 180C) is carried out during which primary and intermediate precursors undergo important thermal degradations. These Maillard reactions lead to the formation of a great number of volatile substances responsible for the coffee aroma (around _______ components)
enzymatic degradations
roasting
700
Fermentation in tea =
enzymatic oxidation of tannins
letting the tea leaves stay in a moist environment (controlled chambers) in which enzymes are activated, those enzymes will promote __________ of phenolic components and form polyphenolic structures and dimeric structures
oxidation
Tea and coffee are very similar in character both in their composition and in the various steps leading to the production of corresponding beverages. They contain ___________ of the xanthine group such as 1,3,7-trimethylxanthine (caffeine) and 3,7-dimethylxanthine (theobromine) that impart a ___________ to the beverage
alkaloids
bitter taste
Caffeine is the main component of __________ and __________, whereas theobromine is present in relatively large amounts in tea
coffee and tea
What are some aroma precursors in tea: (3)
- amino acids
- carotenoids
- lipids
For teas that require oxidation, the leaves are left on their own in _________________ room where they turn progressively _________. This is accompanied by agitation in some cases. In this process the chlorophyll, carotenoids, lipids in the leaves are enzymatically broken down, and its _________ are released or transformed . This process is sometimes referred to as fermentation on the tea industry.
climate-controlled
darker
tannins
The tea producer may choose when the oxidation should be stopped, which depends on the _____________ in the final tea as well as the weather conditions (heat and humidity). For light oolong teas this may be anywhere from ______ % oxidation, in darker cooling teas _____ and in black teas _____ oxidation
desired qualities
5-40
60-70
100
The black tea aroma is a typical example of the important changes induced by ______________. Three groups of substances are involved as flavor precursors: ____________________. Other components of biological matter which contribute to thermal degradation, may also act as precursors.
- fermentation/oxidation
- polyphenols (mainly flavanols)
- carotenoids
- unsaturated fatty acids (linoleic acid)
The ____________ oxidation constitutes one of the important factors contributing to tea flavor.
carotene
Name some carotenoids present in fresh tea leaves:
- theoxanthin
- lutein
- violaxanthin
- ionone
The analysis of the black tea aroma reveals the presence of a great number of substances arising from carotene oxidation such as: play a preponderant role in black tea aroma
- dihydroactinidiolide
- theaspirone
T or F: enzymatic oxidation reactions are more controlled whereas thermal oxidation reactions produce a wide variety of products
T
The carbonyl compound formation under the action of ___________ upon C-18 unsaturated fatty acids of lipids contained in leaves and fruits of various plants has been the subject of many studies
lipoxygenase
Researchers using tea leaf chloroplasts showed that 14C-labelled linolenic acid is converted into ________________________. It is described as having a coarse vegetable-like aroma
12-oxo(E)-dodecen-10-oic acid
(alpha-amino acids and sugars in tea): The changes occurring during the fermentation process may account for the formation of ____________________ by amino acid degradation
aldehydes
What is the most common amino acid in tea:
Theanine (N-ethyl glutamine)
During the next firing step (tea), sugar and amino acid interactions are responsible for the formation of the following heterocyclic compounds:
- furans
- pyrroles
- pyridines
- pyrazines
- oxazoles
- thiazoles
- quinolines
T or F: In the solid extract of tea, 6.52% of total sugars are present including fructose (2.0%), glucose (1.9%), sucrose (1.6%), meso-inositol (0.5%), raffinose (0.3%) and maltose (0.1%).
T
___________________, these two are important reactive compounds which have been found to be present in tea aroma, contribute to the formation of sulphur-containing heterocyclic compounds (thiophenes, thiazoles, dithiolanes, etc)
hydrogen sulphide and dimethyl sulphide
________________ which accounts for 7% of the solid extract, is not practically affected during the preparation of the black tea. On the other hand, it has a significant effect on the astringency taste of the infusion due to its complexation
Caffeine (alkaloids)
_________________ on the black tea polyphenols are the specific sites involved in the complexation with caffeine
The galloyl groups
What is the most important dimeric structure (polyphenol) in tea:
theaflavins
Compounds called catechins are the building blocks of ____________________; they are oxidized to produce theaflavins and thearubigens
black tea polyphenols
T or F: theaflavins comprise 3-5% of black tea and are responsible for its red-orange appearance
T
T or F: The compounds in tea derived from catechins can have antioxidant effects on the body - research has shown these could have beneficial effects on cardiovascular health
T
It has been suggested that ____________ proteins in milk could bind to polyphenols and as a result prevent their antioxidant effects
casein
The composition of roasted coffee not only varies according to the origin of green coffee but also the technique used, the degree of roasting and the _______________
roasting time
___________________ are responsible for modifications which lead to the emanation of off-flavors or a deterioration of aroma itself
seed storage and humidity
What are the main chemical groups of precursors involved during coffee roasting:
- carbohydrates/sugars
- proteins/amino acids
- amines/tryptamines
- phenol acids
- trigonelline
- non-volatile acids such as citric acid
Carbohydrates and sugars are equivalent to ___________ of the green coffee bean weight. These carbohydrates are highly polymerized water-soluble molecules whose components are ___________ and ___________
40-50%
mannose and galactose
