Romeo T. Toledo

Modification of technological properties of fish protein concentrates

Fish protein concentrates are mixtures of cross-linked and aggregated molecules of different muscle proteins. The final conformation of the components of the mixtures is formed as a result of procedures applied to convert the raw materials into a product of desirable and stable sensory properties, containing less than 0.1% of lipids. To achieve this end usually extraction with hot organic solvents, mainly isopropyl alcohol and 1,2-dichloroethene, followed by air drying are employed. These conditions bring about denaturation of many of the proteins followed by aggregation of the molecules due to the interaction of reactive functional groups in extended polypeptide chains. In the final product a large proportion of hydrophobic groups is exposed to the solvent and the proteins exhibit an extremely low water affinity. Such concentrates, although valuable as protein supplements, have only limited suitability as active components of various processed foods, as they have poor technological value. They are insoluble or have a very low water dispersibility and swelling ability, do not form gels after heating, or have any significant fat-emulsifying capacity. Changing the dissociation or number of ionic groups of the molecules prior to extraction, e.g., by acidifying or acylating, can partially reduce the denaturing effect of heat and organic solvents and thus improve the functional properties of the product. An upgrading of the quality of concentrates produced by hot extraction can be achieved by partial enzymatic or chemical deaggregation, hydrolysis followed by the plastein reaction, or formation of suitable derivatives. The best results have been obtained by partial hydrolysis of acylated proteins or precipitation of the aggregated products using sodium hexametaphosphate. The functional properties of such products are comparable to those of vegetable protein isolates used as meat extenders. Various proteins of high technological value can be also obtained by enzymatic hydrolysis of the raw material, followed by separation of the lipids without organic solvent extraction. Such products, however, have a distinct odor and flavor and must be stabilized because of residual lipids.

Thermal Process Calculations

Inactivation of microorganisms by heat is a fundamental operation in food preservation. The concepts presented in this chapter are applicable not only in canning but in any process where heat is used to inactivate microorganisms and induce chemical changes which affect quality. The term sterilization, as used in this chapter, refers to the achievement of commercial sterility, defined as a condition in which microorganisms which cause illness, and those capable of growing in food under normal nonrefrigerated storage and distribution, are eliminated.

Rheological Properties of Banana Puree at High Temperatures

Abstract The rheological behavior of banana puree was determined using a dynamic stress rheometer with a pressure couette fixture, which allowed experiments to be conducted at high temperature. The pressure couette was pressurized with compressed air to 206.8 kPa (gage pressure) and experiments were carried out at temperatures ranging from 30 to 120°C. The shear stress values ranged from 10 to 170 Pa and the shear rate values from 10−5 to 103 s−1. The model that best fitted the experimental data at all temperatures was the Herschel-Bulkley model. There was a usual tendency for the apparent viscosity to decrease with increasing temperature but an increase in apparent viscosity with increasing from 50 to 60°C and from 110 to 120°C was found. This could be due to interaction of polysaccharides present in banana puree. There was a slight difference between the apparent viscosity values for increasing shear stress sweeps and those for the decreasing shear stress sweeps suggesting time dependency of the rheological behavior. Models were proposed to correlate the parameters of the Herschel-Bulkley model and viscosity with temperature.

Evaluation of Liquid Smoke Treated Ready-to-Eat (RTE) Meat Products for Control of Listeria innocua M1

Liquid smoke fractions (S1, S2, S3, and S4) were applied on ready-to-eat (RTE) meat products to control the growth of inoculated Listeria innocua M1. Turkey rolls and roast beef products were dipped in liquid smoke, surface inoculated with L. innocua M1 (10(2) CFU/25 cm(2) RTE meat surface), vacuum packaged, and stored at 4 degrees C. Section 8.5 of USDAs detection and isolation procedure for L. monocytogenes was employed in conjunction with a Micro-ID system for L. innocua M1 identification (ID). Products treated with smoke fractions S1, S2, and S3 were negative for L. innocua M1 at 2 and 4 wk during incubation at 4 degrees C. Products treated with S4 were positive for L. innocua M1 immediately following inoculation and after storage for 2 and 4 wk. Smoke fractions S1, S2, and S3 exhibited pH values lower than 4.6, acidity values higher than 1.5%, and carbonyl concentrations higher than 110 mg/mL. All liquid smoke fractions contained similar phenol concentrations (0.3 to 0.6 mg/mL), suggesting that phenols may have a limited role in the bactericidal effects of liquid smoke fractions against specific microorganisms.

Flow of Fluids

Fluids are substances that flow without disintegration when pressure is applied. This definition of a fluid includes gases, liquids, and certain solids. A number of foods are fluids. In addition, gases such as compressed air and steam are also used in food processing, and they exhibit resistance to flow just as liquids do. In this chapter, the subject of fluid flow will be discussed from two standpoints: (1) the resistance to flow and its implications for the design of a fluid-handling system and (2) evaluation of the rheological properties of fluid foods.

Gases and Vapors

Gases and vapors are naturally associated with foods and food processing systems. The equilibrium between food and water vapor determines the temperatures achieved during processing. Dissolved gases in foods such as oxygen affect shelf life. Gases are used to flush packages in order to eliminate oxygen and prolong shelf life. Modified atmospheres in packages are used to prolong the shelf life of packaged foods. Air is used for dehydration. Gases are used as propellants in aerosol cans and as refrigerants.

Microbial Inactivation Kinetics in Soymilk during Continuous Flow High-Pressure Throttling

The thermal resistance of Clostridium sporogenes PA 3679 ATCC 7955 was determined in soymilk (pH 7) and 0.1% peptone water (pH 7) by the capillary tube method. In the continuous flow high-pressure throttling, the temperature of soymilk increased due to instantaneous pressure release and the additional heat was supplied by a heat exchanger to achieve the set temperature. The soymilk was immediately cooled after a short preset hold time to below 40 degrees C. A significant increase in the heat resistance was observed in C. sporogenes spores when heated in soymilk in comparison to 0.1% peptone water. The D(121)-value for spores in soymilk was approximately 3-folds higher than peptone water. The z-value was also much higher in soymilk as compared to that in 0.1% peptone water. Continuous flow high-pressure throttling (HPT) from 207 or 276 MPa to atmospheric pressure reduced the microbial populations in inoculated soymilk up to 6 log cycles when the holding times were 10.4, 15.6, and 20.8 s and the process temperatures were 85, 121, 133, and 145 degrees C, respectively. The sporicidal effect increased as the operating pressure, time, and temperature were increased. More injured spores were found at 207 MPa than at 276 MPa, indicating that lower pressure caused cell injury whereas high pressure caused cell death.

Rheological and Ultrastructural Properties and Particle Size Distribution of Soymilk as Affected by Processing Methods

Soymilk was prepared from boiled and unboiled comminuted suspensions of dehulled soybean and water using pressurized homogenization (one pass and two pass). Particle size showed significant differences between soymilks homogenized by one pass and two pass. Apparent viscosities and total solid contents showed significant differences between boiled and unboiled treatments. Soymilks exhibited pseudoplastic and thixotropic behavior and Arrhenius model was fitted to express temperature dependence of apparent viscosity. Microscopic images showed hydrated, separated, uniformly distributed, and homogeneous particles in boiled two-pass soymilk as they were disrupted easily and it was selected as the best treatment for processing soymilk containing all of the soybean solids.

Kinetics of Chemical Reactions in Foods

Chemical reactions occur in foods during processing and storage. Some reactions result in loss of quality and must be minimized, while others produce a desired flavor or color and must be optimized to obtain the best quality. The science of kinetics involves the study of chemical reaction rates and mechanisms. An understanding of reaction mechanisms coupled with quantification of rate constants will facilitate the selection of the best conditions of a process or storage so that the desired characteristics will be present in the product.

The Use of a Submerged Microfiltration System for Regeneration and Reuse of Wastewater in a Fresh-cut Vegetable Operation

Abstract Wash water from a fresh‐cut vegetable processing plant was filtered using a submerged microfiltration module containing PVDF membranes. The unfiltered water and permeate were analyzed and the flux and fouling rate were monitored in an effort to find the ideal parameters for the system. The study found the system had a pure water rate of 24 L/hm2 which was reduced to 19 L/hm2 after 6 hours with cleaning, when run at 40–50 kPa. The ideal cleaning regime was found to be every 1 hour for a period of 120 seconds at 200 kPa.