Heated off-flavor

Very limited information has been published on this subject. Using a sensory panel which employed quantitative descriptive analysis, Rouseff (2 ) was able to demonstrate that heated off-flavor was the major quality factor in determining the perceived quality of the juice. Some flavor descriptors used in this study are shown in Figure 3. Panelists evaluated each flavor descriptor using a 10-cm line anchored with weak and strong on the ends, and overall quality, previously defined using a 100-point... 

Fats act as precursors to flavor development by interacting with proteins and other ingredients when heated. Off-flavors are not normally perceived in full-fat systems because most of them are fat-soluble. However, in the absence of fat, the vapor pressure of the aroma chanical in water is increased, resulting in a very intense perception of the off-flavor chemical. Flavor release is a critical factor governing smell and taste. The majority of flavor components are dissolved to some extent in the lipid phase of food— releasing the flavor slowly in the mouth and resulting in a pleasant aftertaste [75]. 

Chemical bleaching is never used on oils intended for edible use because it oxidizes unsaturated fatty acids to cause off-flavors. However, it does find wide usage for specialty linseed oil, for the paint industry, and fatty chemicals such as sorbitan esters of fatty acids and sodium stearoyl lactylate. Residual peroxide is destroyed by heating above its decomposition temperature. 

Vacuum Treatment. Milk can be exposed to a vacuum to remove low boiling substances, eg, onions, garlic, and some silage, which may impart off-flavors to the milk, particularly the fat portion. A three-stage vacuum unit, known as a vacreator, produces pressures of 17, 51—68, and 88—95 kPa (127, 381—508, and 660—711 mm Hg). A continuous vacuum unit in the HTST system may consist of one or two chambers and be heated by Hve steam, with an equivalent release of water by evaporation, or flash steam to carry off the volatiles. If Hve steam is used, it must be cuUnary steam which is produced by heating potable water with an indirect heat exchanger. Dry saturated steam is desired for food processing operations. 

Irradiation. Although no irradiation systems for pasteurization have been approved by the U.S. Food and Dmg Administration, milk can be pasteurized or sterilized by P tays produced by an electron accelerator or y-rays produced by cobalt-60. Bacteria and enzymes in milk are more resistant to irradiation than higher life forms. For pasteurization, 5000—7500 Gy (500,000—750,000 tad) are requited, and for inactivating enzymes at least 20,000 Gy (2,000,000 rad). Much lower radiation, about 70 Gy (7000 tad), causes an off-flavor. A combination of heat treatment and irradiation may prove to be the most acceptable approach. 

The increased use of tanks for the storage of raw milk on the farm between pickups has introduced the danger of potential off-flavor development caused by lipases that are produced by certain microorganisms (psychrotrophs) at low temperatures. The exocellular lipases of psychrotrophic bacteria are extremely heat resistant, and although the microorganisms are killed, the enzymes survive pasteurization and sterilization temperatures. Rancidity may become noticeable when cell counts exceed 106 or 107/ml. Downey (1975) has summarized the potential contribution of enzymes to the lipolysis of milk (Table 5.1). 

Heat-Resistant Lipases. The heat-resistant lipases and proteinases and their effects on the quality of dairy products have been reviewed (Cogan 1977, 1980). Several reports have linked the lipases from bacteria with the off-flavor development of market milk (Richter 1981 Shipe et al. 1980A Barnard 1979B). The microflora developing in holding tanks at 4°C [and presumably in market milk stored at 40°F (Richter 1981)] may produce exocellular lipases and proteases that may survive ordinary pasteurization and sterilization temperatures. Rancidity of the cheese and gelation of UHT milk appear to be the major defects caused by the heat-resistant enzymes. 

Fluid milk is commonly subjected to a combination steam injection/in-fusion and vacuum flash evaporation process to remove volatile off-flavor compounds. The process is designed to remove the same amount of water by the flash treatment as is added during steam injection/infu-sion, so that the composition of the milk remains unchanged. This treatment is most effective for removing volatile, water-soluble flavor compounds, such as those from weeds and feed consumed by the cow. The additional heat from this process usually provides further improvement in product shelf life. 

Two types of enzymes in milk are important those useful as an index ol heat treatment and those responsible tor bad flavors. Phosphatase is destroyed by the heat treatments used to pasteurize milk hence its inactivation is an indication of adequate pasteurization. Lipase catalyzes the hydrolysis of milk fat which produces rancid flavors. It must be inactivated by pasteurization or more severe heat treatment to safeguard the product against off-flavor development Other enzymes reported to have been found in milk include catalase, peroxidase, protease, diastase, amylase, oleinase. reductase, aldehydrase. and lactase. 

The alert panel supervisor will also come to know about each regular panelist s ability to detect the many off-flavors that could possibly occur in citrus products. Of primary concern, other than the common sweet and sour flavor attributes, are the panelists abilities to specifically identify (a) bitterness (naringin and/or limonin induced), (b) heated, processed or pumpout off-flavor, (c) excess peel oily, (d) excess and/or poor essency flavor, and (e) the following off-flavors cardboard, tallowy, castor oil, diacetyl or buttermilk, green or immature, overmature or stale fruit, and spoiled fruit. 

Apparently like so many other flavor attributes of citrus products, heated, processed or pumpout type of off-flavors vary considerably in individual threshold and tolerance levels. The author, for example, possesses both a low threshold and tolerance for this particular off-flavor in any type of citrus product. 

Potato taste is not characterized by one of the primary taste sensations. Especially sweet, sour or bitter notes are considered off-flavors. However, free amino acids and 5 -nucleotides are important compounds that convey an agreeable basic taste to potato products. The amino acids occur naturally in free form the 5 -nucleotides are liberated during the heat preparation of potatoes by a specific enzymatic degradation of RNA. Starch forms a matrix for all potato preparations. Although it is tasteless, is has an influence on taste quality due to textural characteristics, and due to its pronounced capability to form stable complexes with flavor compounds either in a thermal gradient or under isothermal conditions. 

Pre-heating milk to 90-95°C for 1 min to maximize—SH groups and an acceptable level of cooked off-flavor... 

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