Paul S. Dimick

Review of apple flavor: state of the art

The retention flavor is of utmost importance during the harvesting, handling and/or further processing of apples. The complexity of the natural flavor of the apple or essence derived therefrom is attributed in part to the variety, post-harvest treatment, storage, and process manipulation. Some 266 volatile components isolated from apples include alcohols, esters, aldehydes, ketones, ethers, acids, bases, acetals, and hydrocarbons. This review is a survey of the literature published during the last 10 to 15 years and includes the contribution of peel to flavor, postharvest quality indices related to flavor, storage and dehydration effects on flavor, juice extraction methods, sensory evaluation, and volatile separation and identification techniques.

Lipid and hardness characteristics of cocoa butters from different geographic regions

Twenty-four commercially pressed cocoa butters and 39 laboratory solvent extracted cocoa butters were evaluated. A rapid method using differential scanning calorimetry (DSC) was used to evaluate the hardness of small quantities of cocoa butter. In the DSC thermogram of a quenched sample, the percentage area under the polymorph II endotherm had a positive correlation (r=0.74) with the mechanical hardness. Soft cocoa butters were characterized by high POO, SOO content (P=palmitic acid, O=oleic acid, S=stearic acid), high iodine value, low percentage, area under the polymorph II endotherm from the DSC scanning, and low SOS. Hard cocoa butters displayed opposite characteristics. In general, South American cocoa butters were the softest and had a 37.03 iodine value, a total of 9.1% POO and SOO, and a 26.4% area under the polymorph II endotherm. Cocoa butters from Asia and Oceania were the hardest and had a 34.74 iodine value, a total of 4.1% POO and SOO, and a 35.65% area under the polymorph II endotherm. North and Central American and African cocoa butters were intermediate in hardness characteristics.

Dynamic crystallization of cocoa butter. I. characterization of simple lipids in rapid- and slow-nucleating cocoa butters and their seed crystals

Six cocoa butters with different crystallization induction times and their seed crystals were analyzed for simple lipid composition. The rapid-nucleating cocoa butter samples had higher concentrations of 1-palmitoyl-2-oleoyl-3-stearoylglycerol and 1,3-stearoyl-2-oleoylglycerol (SOS), and lower concentrations of the diunsaturated triacylglycerols, 1-palmitoyl-2,3-oleoylglycerol and 1-stearoyl-2,3-oleoylglycerol, as well as higher stearic acid concentrations within their diacylglycerol fractions when compared to the slow-nucleating samples. At the early stages of crystallization, under agitation conditions at 26.5°C, cocoa butters solidified into two fractions, high-melting and low-melting. The low-melting fractions were composed of polymorphs IV and V of cocoa butter, as indicated by the onset melting temperatures of the endotherms from differential scanning calorimetry. The high-melting fractions, which had wide melting ranges, had peak maxima of 38.5–52.2°C. Seed crystals isolated at the early stage of crystallization were characterized by high concentrations of complex lipids, saturated triacylglycerols, saturated fatty acid-rich diacylglycerols, and monoacylglycerols. The rapid-nucleating seed crystals had higher concentrations of SOS when compared to their respective cocoa butters. The slow-nucleating seed crystals did not exhibit this characteristic.

Lipid composition of high-melting seed crystals formed during cocoa butter solidification

High-melting seed crystals which form during the early stages of cocoa butter solidification possess a lipid composition different than the cocoa butter from which the seed crystals were grown. Significantly large quantities of glycolipids, 11.1%, and phospholipids, 6.6–8.1%, were found in the high-melting seed crystals along with a dramatic decrease in the simple lipid class. The fatty acids comprising the simple lipid fraction of the seed crystals were considerably more saturated than the fatty acids present in the same fraction of the original cocoa butter. The increase in the degree of saturation was reflected in the triacylglycerol composition. Cocoa butter samples were predominantly monounsaturated triacylglycerols while the seed crystal samples were mainly trisaturated triacylglycerols. The elevated melting point (60–70°C) of the seed crystals was due to the presence of higher melting complex lipids as well as to the increase in saturated triacylglycerol species. As a result of the evidence provided, the high-melting seed crystal is indeed a distinct crystalline entity and not an additional polymorphic form of cocoa butter.

Dynamic crystallization of cocoa butter. II. Morphological, thermal, and chemical characteristics during crystal growth

After an induction period, crystallization of cocoa butter under dynamic conditions at 26.5°C occurs in two stages, primary and secondary. The primary stage involves nucleation, crystal growth, aggregation, and sintering. Crystals formed during the primary stage were slightly or non-birefringent, and had long, irregular-shaped filaments. The secondary stage was initiated by the formation of spherulites. Total crystallization time may depend upon the crystal growth rate in the primary stage and the time that coca butters take to form the spherulitic crystals in the secondary stage. After the spherulitic crystals formed, the crystal growth rates were rapid. Cocoa butters crystallized into two fractions during the primary and secondary stages. The low-melting fractions had onset melting temperatures similar to those of polymorphs IV and V of cocoa butter. The high-melting fractions, which were observed at the latter stages of crystallization, had differential scanning calorimetry endotherms with peak maxima at approximately 34–36°C (Form VI). The concentrations of 1,3-stearoyl-2-oleoylglycerol (SOS) in the crystals during growth were higher than those in the original cocoa butter. As crystallization progressed, crystals increased in their proportions of SOS in the triacylglycerol fraction. Concentrations of the C18 free fatty acids were lower during early crystallization as compared to the original cocoa butter.

Isolation and thermal characterization of high-melting seed crystals formed during cocoa butter solidification

Seed crystals which formed during early stages of cocoa butter solidification have been isolated and determined to have extremely high melting points. The melting points of the seed crystals generally exceeded 60°C, in contrast to cocoa butter, which melts between 30–35°C. In addition, the melting point of the seed crystals decreased as a function of crystal growth time. Evidence suggests that the high-melting seed crystal is not an additional polymorphic form of cocoa butter, but rather a distinct crystalline entity. Consequently, a unique compositional make-up is suspected as being responsible for the elevated melting point. A technique to separate seed crystals from the molten cocoa butter mass has been developed. The procedure has been shown not to alter the thermal and compositional properties of the isolated seed crystals.

Thermal and compositional properties of cocoa butter during static crystallization

Studies were conducted using differential scanning calorimetry (DSC) and high performance liquid chromatography (HPLC) to determine the thermal properties and glyceride composition of cocoa butter crystals formed under static conditions. In addition to these studies, visual characterization of the crystallites was obtained with polarized light microscopy (PLM). Crystals were formed under controlled static or motionless conditions at formation temperatures of 26.0, 28.0, 30.0, 32.0 and 33.0 C. Preparatory techniques were developed using laminated polyethylene with plastic hoops in order to grow the crystals for isolation and visual identification by PLM prior to DSC assay. Cocoa butter was also crystallized from liquid oil directly in the DSC pans prior to thermal assay. At each crystal formation temperature (26–33 C), various crystallite types grew, each with varying triglyceride composition (PLiP, POO, PLiS, POP, SOO, SLiS, POS, SOS, SOA). As an example, the ‘feather’ and ‘individual’ crystals formed at 26.0 C exhibited significant increases in SOS and significant decreases in POP compared to the original butter. It was determined that the original amount of SOS significantly increased in the cocoa butter crystallite as the incubation temperature increased from 26–32 C.

Phospholipid composition of lipid seed crystal isolates from ivory coast cocoa butter

Seed crystals isolated from Ivory Coast cocoa butter were shown to differ in chemical and thermal characteristics from solidified Ivory Coast butter. Higher concentrations of complex lipids in the seed crystals have led to speculation on the role these polar molecules play in lipid crystallization events. Phospholipids separated from lipid seed crystal isolates were twelve-fold more concentrated than the original cocoa butter. Seed crystals contained 3.99% phospholipids while cocoa butter samples contained 0.34%. Phosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, lysophosphatidylcholine, phosphatidylserine, and phosphatidic acid were identified in cocoa butter with phosphatidylcholine (37.7%), phosphatidylglycerol (27.3%) and phosphatidyl-ethanolamine (15.6%) being the major phospholipid constituents. Two phospholipids not previously reported in cocoa butter were identified as phosphatidylglycerol and diphosphatidylglycerol based on co-migration of standards. Cocoa butter and its seed crystals contained the same phospholipid entities; however, individual phospholipids differed significantly in concentration. Phosphatidylethanolamine (30.4%) and phosphatidylcholine (30.2%) were the major phospholipids in seed crystal samples. Fatty acid composition of cocoa butter and seed crystal phospholipids were found to be similar, with the exception of myristic, stearic and oleic acids. Myristic acid was three-fold higher in phosphatidylglycerol and phosphatidylethanolamine in the seed crystals, whereas stearic acid was significantly lower in the seed crystals when compared to the cocoa butter. Concentrations of oleic acid were twice as high in seed crystal phosphatidylethanol-amine and almost four times as high in seed crystal phosphatidylcholine than in corresponding cocoa butter samples. The possible role phospholipids play in seed crystal development and in crystallization events is discussed.

Photochemical Effects on Flavor and Nutrients of Fluid Milk

Abstract Acceptance of fluid milk by the consumer is determined to a great extent by quality measures of flavor, shelf life and nutritional value. A major flavor defect and nutrient loss factor associated with todays marketing environment of fluid milk is attributed to the extended exposure to fluorescent light used to illuminate display cases. Criteria for the photochemical reactions to occur require the presence of light, protein, riboflavin and oxygen. This review will discuss the problem, flavor development and container relationships, origin of the light-induced flavor, destruction of vitamin A, B2 and C and their relationship to off flavor formation, and the effects of fluorescent light on milk proteins and amino acids. Awareness of the potential problems, as defined here for milk systems, may be of concern in other food commodities sold through similar distribution and marketing channels.

Evaluation of Fluorescent Light on Flavor and Riboflavin Content of Milk Held in Gallon Returnable Containers1

Five 1-gal. retail containers were evaluated for their protection of homogenized milk against development of light-induced flavor and degradation of riboflavin. These were clear polycarbonate, tinted polycarbonate, high-density polyethylene, and glass returnable containers and an unprinted fiberboard non-returnable container. All containers were held in a commercial sliding door display case at 7 ± 1 C illuminated to 1076 lx with a fluorescent lamp up to 72 h. Sensory evaluation was conducted by a trained panel using hedonic 9-point scoring and magnitude estimation scale techniques. Riboflavin was determined by the fluorometric method. An evaluation of the containers demonstrated that there was a significant difference (P < .05) in preference and degree of light-induced flavor between the milk held in clear polycarbonate and glass compared to the control milk after 12 h of exposure. Milk held in high-density polyethylene was significantly different in preference from the unexposed control following 12 h when evaluated by the hedonic method; however, 24 h of exposure were needed to demonstrate a significant difference in the degree of light-induced flavor using the magnitude estimation technique. The tinted polycarbonate container, which is fabricated with a blocking agent that inhibits transmission of light at 380-480 nm, provided the milk with greatest protection of the returnable containers against development of the off-flavor. Milks exposed in fiberboard and also milks in the five containers held in the dark were not significantly different from the unexposed control. The milks held in glass demonstrated significant losses in riboflavin following exposure.