A review of corn masa processing residues: Generation, properties, and potential utilization
Introduction
Due to mounting economic and environmental concerns, landfilling of agricultural and food processing waste materials has declined in recent years, and alternative disposal methods are being increasingly implemented. Principal options currently include reprocessing, recycling, incinerating, composting, producing biomass energy, applying to land as soil conditioners, and reusing as livestock feed additives, which is an option that can include either direct feeding of the waste products or feeding the byproducts after additional value-added processing (Bohlsen et al., 1997, Derr and Dhillon, 1997, Ferris et al., 1995, Wang et al., 1997).
Rosentrater (2001) promulgated a seven-step approach to successful byproduct development and utilization efforts. This methodology included identifying, quantifying, characterizing, developing, analyzing, optimizing, and modeling the waste stream under investigation. Identifying, the first step in this byproduct utilization philosophy, encompasses identifying the specific waste or byproduct stream of interest. This typically entails examining production processes in detail, so that major (and minor) byproduct streams can be identified and effective removal points can be discerned. In recent years, several surveys of food processing industries in various regions throughout the United States have been conducted and have identified many current food processing waste streams that require addressing (Bohlsen et al., 1997, Flores and Shanklin, 1998, Flores et al., 1999, Goldstein and Glenn, 1997, Nelson and Flores, 1994, Youde and Prenguber, 1991). Quantifying includes physically measuring how much waste material is produced by a given production process, either in terms of a volumetric or a mass basis, and determining what fraction of process inputs are actually converted into waste (i.e., calculating process efficiencies). Characterizing involves determining various key physical, nutritional, and chemical properties of the waste stream. Vital physical properties include moisture content, water activity, density, yield stress, apparent viscosity, thermal conductivity, thermal diffusivity, heat capacity, and drying behavior. Essential nutritional and chemical properties include pH, protein, carbohydrate, fat, ash, fiber, vitamin, and mineral contents. Characterization of byproduct materials is important because it provides data that are required for livestock diet formulation, design of equipment and processing facilities, and optimization of unit operations such as blending, mixing, separating, drying, extruding, heating, freezing, pumping, and conveying (Ferris et al., 1995, Stroshine and Hamann, 1995). Developing entails investigating potential value-added uses for the byproduct materials and is actually at the heart of byproduct development efforts. Activities during this phase could employ multiple unit operations, such as blending with another material, extruding or drying the byproduct, and then shipping for use as a livestock feed additive; it may involve composting for later use as a soil conditioning amendment; and it might even encompass developing an entirely new industrial product, and also a new market, for the byproduct material. No byproduct development study is complete, however, without analyzing the economics associated with each proposed reprocessing or reuse alternative (Derr and Dhillon, 1997). Ultimately, disposal techniques are only attractive to processors if they are not more expensive than landfilling, the traditional disposal mechanism for many byproduct streams. At the optimizing stage, it is vital to examine production processes to determine if any alterations can be made to improve process efficiency and, thus, to reduce the quantity of waste materials produced at the source of generation. Not only can this reduce waste remediation costs, but it can also increase production profitability, and should actually be an integral component to a manufacturer’s continuous quality improvement program. Finally, after all of the groundwork has been completed and enough information has been gathered and analyzed, computer modeling should be used as a tool to simulate process operations and to examine the effects of subsequent alterations on the production systems involved.
Over the years, many byproduct research efforts have utilized some, or even all, of the aforementioned components. In fact, a number of these studies have focused on the development of value-added food, feed, and industrial applications from various segments of the grain processing industry. Particular attention has been given to corn wet milling, dry milling, brewing, and distilling byproducts, primarily due to their large industrial scales. Corn masa milling, however, is one sector of the grain industry that, although it is a considerably smaller industry segment, does generate large quantities of waste materials. To date, it has been largely ignored in terms of byproduct disposal methodologies and alternatives. Because the demand for corn masa-based products has been greatly increasing in the United States during the last several years, subsequent value-added applications must be effectively pursued for these materials soon.
Consequently, the objective of this paper was to thoroughly examine and review the published literature, and to amalgamate and summarize the current state of minimal, disparate knowledge regarding masa byproduct streams. Published literature pertaining to corn masa processing was comprehensively sought out and thoroughly examined for information regarding masa production waste streams. The information gleaned from this endeavor was then categorized vis-à-vis the aforementioned byproduct utilization approach, and in so doing, not only was a thorough review of current knowledge regarding masa processing residues developed, but current gaps in the knowledge base were also identified, and as such, several avenues for potential research work were discerned.
Section snippets
Corn masa processing residues
Corn masa is used in the production of corn chips and snacks, taco shells and tortilla chips, and tortillas, which have been for centuries, and in fact, to this day still are, a staple in the diets of Mexican and Central American peoples (Bressani et al., 1958, Cravioto et al., 1945, Krause et al., 1992a, Vaillant, 1962). In some Latin American countries, tortillas alone can provide up to 70% of total daily caloric and up to 50% of total daily protein, calcium, iron, and zinc intake (Chavez,
Residue generation
Nejayote is an organically rich waste water stream that contains a high concentration of solid materials. These solids consist of corn dry matter which is lost during processing. Over the years, only 12 studies have investigated nejayote generation and reported nixtamalization losses have ranged from 0.5% to 14.5% of the original corn dry matter. These findings are summarized in Table 1. Also summarized here are reported results for solids concentrations typically found in these waste streams,
Residue properties
Because no viable disposal alternatives have been developed to date, novel reuse strategies for these processing residues must be pursued. Byproduct characteristics, namely physical, nutritional, and chemical properties, will provide essential data that are requisite to developing successful reuse alternatives. Although no single study has established a comprehensive set of data, seven investigations over the years have examined various properties for both nejayote streams and the solids
Prospects for residue utilization
To date, only a few studies have been found that have investigated alternative disposal or reuse options for these byproduct streams. Gonzalez-Martinez (1984) investigated four biological treatment options for nejayote on a laboratory-scale, including activated sludge processing, anaerobic contact processing, submerged aerobic fixed-film cascade reacting, and anaerobic packed-bed reacting. This study determined that the activated sludge and the anaerobic packed-bed reactor systems could
Conclusions
This paper has reviewed generation rates, fundamental properties, and potential utilization strategies for corn masa processing residue streams, which are currently waste materials that are landfilled but require alternative means of utilization. This need will become more acute as the masa industry continues its rapid growth. Retrospectively examining the published literature has yielded limited, but essential, generation and property information for these residuals, and has provided several
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