Biomedical Engineering Reference
In-Depth Information
content, a large proportion of unsaturated fatty acids, and a significantly more active
lipase than that of either barley or wheat.
66
Oats contain antioxidants and oat lipids
are stable in mature, undamaged grains
67
and in sufficiently heat-treated oat prod-
ucts.
68
However, under unfavorable storage conditions or in untreated oat products
lipolytic activity will cause rapid release of free fatty acids (FFA), which may then
be oxidized and cause rancidity. Oxidative rancidity may also be caused by over-
processing.
69
Thus, adequate storage conditions
70
and appropriate heat treatment for
inactivation of lipolytic enzymes before milling of oats
68
are essential in achieving
stable oat products.
71
Because unsaturated FFA in oats are susceptible to oxidation
and many form components with undesirable aroma and taste,
68
analysis of the
amount of FFA may be useful for predicting lipid stability. For oats to be processed
into food products, a maximun FFA level of 5% hexane extractable lipids has been
suggested.
72
FFA in oats enhance formation of bitter compounds.
73
An approach to
overcome the problems produced by the unsaturated FFA is the genetic engineering
of oat crops where the levels of unsaturated FFA are reduced.
53,54
Coffee is one of the most commercially important grains in the food industry.
Coffee comprises a number of different forms, ranging from coffee cherries (berries);
green coffee, which is trade beans that are removed by one of a number of different
process sequences after harvesting; roast coffee, which is the green coffee beans
that are roasted by a heat process, either domestically or commercially, and which
may also be pre-ground; and the coffee beverage, which is the form in which it is
actually consumed. It should also be understood that while coffee cherries/beans
exist in a number of different botanical species within the corresponding genus, only
two are used commercially,
Coffea arabica
and
C. canephora
(robusta in the trade),
and can reflect different characteristics in storage behavior and in their subsequent
coffee products.
74
The greatest interest is in the shelf life of roasted (and ground) coffee, since this
is the form in which coffee is most familiar, together increasingly with instant coffee
to the consumer. Green coffee, roasted coffee, and instant coffee all have two main
divisions of their chemical composition; first, the non-volatile matter, some contrib-
uting to basic taste sensations of acidity, bitterness, and astringency and the remain-
der, composed mostly of carbohydrates and proteins of generally neutral flavor
characteristics; and second, the volatile substances, present in a very small amounts
(ppm levels) but of great significance to overall flavor in the prepared cup of coffee
beverages. In all these coffees, environmental factors of temperature, humidity, and
oxygen exposure strongly determine storage behavior and therefore shelf life,
together with the initial moisture content of the coffee, and its precise composition.
The previously mentioned factors determine the condition or quality of roasted coffee
after given periods of time. The terms “condition” and “quality”, however, are very
much subjective and are not amenable to scientific assessment.
74
Like all other
foodstuffs, roast coffee, and even more rapidly, roast and subsequently ground coffee,
deteriorate with time from their initial state of “freshness” (i.e., after roasting in
roasted coffee), but the actual deterioration has to be assessed on the cupped bev-
erage, prepared under standardized conditions for all samples being compared, by
human senses. Panels of judges are asked to assess changes from “fresh” flavor
quality on numerical scales, and at what point the coffee is no longer “acceptable”
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