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Processing of nutritious, safe and acceptable foods from celss candidate crops
A&. Space Rcs. Vol. 98, No. i/2, pp. (1/2)24~-(1/2)~5~, 1996 Copyright @a1995 COSPAR Printed in Oreat Britain. All rights reserved 0273-I 177/M $9.50 + tmo
Pergamon
0273- 1I77(95)008 W-4
PROCESSING OF N~~~T~OUS, SAFE AND ACCE~A~LE FOODS FROM CELSS CANDIDATE CROPS B. Fu, P. E. Nelson, R. Irvine and L. L. Kanach
ABSTRACT A controlled ecological life-support system (CELSS) is required to sustain life for long-duration space missions, The challenge is preparing a wide variety of tasty, familiar, and nutritious foods from CELSS candidate crops under space environmental conditions. Conventional food processing technologies will have to be modified to adapt to the space ei~vironment. Extrusion is one of the processes being examined as a means of converting raw plant biomass into familiar foods. A nutrition-improved pasta has been developed using cowpea as a replacement for a portion of the durum semolina. A freeze-drying system that simulates the space conditions has also been developed. Other technologies that would fulfill the requiremeilts of a CELSS will also be addressed. INTRODUCTION The development of space food has evolved from tubes and cubes to near Earth-like cuisine over the past 30 years it/, On current missions, spacecraft crews consume foods stored aboard their spacecraft. As the i~uman presence in space increases in duration, in numbers of people, and in distance from Earth, the economics of resupply and sizing of space habitats for storage of life-support items (including food) become major limiting factors. Extraterrestrial and in-flight food processing and packaging become necessary when edible biomass is to be produced in situ. At Purdue University’s NASA Specialized Center of Research and TraiIling ESCORTS in bioregenerative iife-suppo~, pllotosyllt~leti~ plant crops are proposed to be the primary candidates for biomass production in a controlled ecological life-suppo~ system (CELSS) 121, based on the fact that people on Earth can live on pure vegetarian diets, Plant species growing in a CELSS must provide a nutritionaIly and psychologically adequate diet for human il~habitaitts living on the moons free-space se~lements, or other planets. Alternative biological systems (aquatic species, algae, and mushrooms) may also play a role in a future CELSS, especially for protein production and waste conversion /3/. One of the basic requirements for food processing is to make the foods taste good. Military experiences have shown that troops will not necessarily eat “enough of anytIling” when they are hungry if the food does not taste good or if they are tired of the food. Nutrients are of no value unless consumed. One can not meet the demand by just serving up parts of the candidate crops. The key lies in the utilization of somewhat more complex processes within the overall technological and engineering constraints of the CELSS {Table 1) to produce diversity of products that increase palatability and provide useful functional properties. Other basic requirements and operation requirements for food processing are also listed in Table 1. So far, most effort has been directed to more efftcient biomass production, and less work has been done on the conversion of traditionaily non-edible plant biomass into foods. Karet and Kamarei 141 investigated the feasibiiity of producing a range of engineered or fabricated foods from a limited range of utldifferentiated major food components. The question is how to develop spacecompatible food fabrication processes. In another study, Karel and Nakhost /S/6/ isolated high quality proteins from green algae and incorporated them into several foods, such as muffins and fettuccine. Organoleptic acceptability of these so-called “novel products” made from nontraditional food sources, however, has been a major challenge. Achieving acceptance continues to challenge food scientists and technologists.
w2)241
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H. Fu el al.
TABLE 1 Requirements
and constraints
of food processing
in space
1 Constraints Space environment Hardware weight and volume Power Crew time Unconventional biomass Plant toxicants/antinutrients Volatiles and chemicals Dust and particulates ~icroorganisIns Packaging materials 1 Waste disposal
Requirements Safe Nutrjtjous Palatable Versatile Familiar Storage stability Easy to prepare Easy to operate Easy to clean-up Reliable and flexible Clean-room processing
Our objective is to develop a space-compatible system that can produce safe, nutritious and palatable foods from CELSS candidate crops. In this paper, processing characteristics of the CELSS candidate crops and adaptability of conventional food processing technologies to the space environment will first be discussed. Results from two case studies, extrusion of cowpea-substituted pasta and freeze-drying of potatoes under simulated space atmospheric conditions, will be presented. Finally, some potential technologies with possible applications in a CELSS will be addressed briefly. PROCESSING
CHARACTERISTICS
OF CELSS CANDIDATE
CROPS
Some CELSS candidate crops and their characteristics are listed in Table 2. These species are selected mainly based upon criteria such as nutritional quality, versatility of food products they can produce, as well as the amount of processing necessary to render the products edible /7/. Lettuce. Tomato and Radish Lettuce, tomato, and radish are considered salad crops. They are good sources of vitamins and minerals. When eaten raw, all three are considered detergent foods, important to dental health. Tomato is also a standard item in soup and the base for many delightful sauces and dressings. It can be eaten fresh or can be cooked in many forms: stewed, fried, and baked. These materials are not considered protein sources and usually do not contain significant amount of antinutrients or natural toxicants. Both lettuce and radish should be stored under refrigeration with very high humidity. Tomatoes should not be refrigerated until such time as they are fully ripened. The tomato plant has much less edible portion that do the other two crops since its stems, leaves and roots are inedible. That is, tomato has a relatively low harvest index (fraction of total biomass that is edible). Rice and Wheat The major col~stituent of cereal grains is starch. Rice contains considerably less protein than wheat, but its protein has a somewhat higher biological value. These proteins are deficient in lysine and tryptopllail. The vitamin and lipid contents depend upon the degree of refining, and cereal grains contain antinutrients, such as phytates and protease inhibitors, that could become significant if not properly processed. Cereal crops in general have a low harvest index. Thus, utilization or treatment of the nonedible materials is critical to the success of a CELSS. The type and quality of products obtained from cereal grains depend on the type and quality of the grain used and its processing. Rice grains are often consumed as whole kernel rice after some type of milling. Rice can also be used for flour or baked goods, but wheat is probably the most versatile of the grain crops as a food. The wheat protein (gluten) has unique elastic and gas retention properties, which are responsible for the ability of wheat to form leavened products and extruded pasta products. It can be processed and served in numerous forms and combinations. Various degrees of refining are required to take full advantage of this crop; however, the degree of refining is constrained by the CELSS
Prcxx=sing
t 112t241
C‘ELSS Foodr
TABLE 2 CELSS candidate crops and their char~cterjstjcs~ CEXpS
Lettuce Tomato Radish Rice Wheat
Main nutrients Fiber, VA, VC, Fe, Ca VC, VA, K, P VC, K, Mg CHO, protein, VBs, MS CHO, protein, VBs, MS Lipid, Protein, CHO
Deficients
~ntin~t~~e~~/toxic~~ts
Main uses
Nitrates Glucasinates Phytates
Salad Salad, juice, sauce Salad, cooking Cooking
Phytates, PI
Bread, pasta
Qif. soymitk tofu, TX phytates, fecfins, saponins, tlatulussoysauce producing ol~gos~cci~arid~s A~ato~i~~s~ Pf . phytates, Oil, roasting, peanut Lipid. protein, CHO Peanut lectins bntter Erucic acid, g~ueosjnat~~ Oif Rapeseed Lipid phytates, goitrogens Phytates. &tins, PI, Leaves for salad. CHO, protein, fiber COWQtXk seed for cooking ~atulus~p~odLicing oligos~ccharides Solanines, lectins, Pf Cooking. baking ct-ra,vc. VBS. Fe, P P~~~to~~~~jns, P1 Sweet paato CHO, VA, VC, MS Met Baking * VA-~~tal~~~l A: VC-vitamin C; VBs-vitamins B; &%+-minerals; CHU~ar~ollj~~drates~ Lys---fysine: Try-tr~ptop~~an~ Cys-cysteine; Thr-threine: Met-methinne; Pf-protease inhibitors
Soybean
environmel~t. Bran and germ disp~s~~/~tili~ation is also an issue. Recently, it becomes common for some people to use whole wheat flour in making bread or other similar products. The tbrcshed whole wheat grains can also be consumzd after parboiling.
of dwmn wheat was found to be higher tvhen harvested at an ear1.v stage of maturity compared to a later stage of maturity or at fulif maturity iii/‘. This finding suggests that further i~lvcsti~atioi~ into the functioI~a~ and ~~utritiona~ advantages of early-harvest wheat could be beneficial to CELSS from more than just a growth-cycle standpoint.
The pm&in ef~~je13cy rario(PER)
Soybean. Peamn, Rapeseed and Cowneg! Soybean peanut. and rapeseed are oiiseeds, They mainly provide lipid, protein3 and car~o~~d~~~~ in the edibie portion. Their prot&s ~~~~ra~~~ are rich ia Ipine but tack s~~f~~-co~~~a~~~~~~ amino acids. OII can be extracted from the oilseeds mecI~a~~~cal~yand is suitable for consu~~pt~or~ as a salad oii, frying medium, bakery ingredient, or many other uses. Fortunately, the soiid residues from the extraction process can be further processed for human consumption. Different Jevels of processing may be involved depending on the final products desired. A variety of products, such as soymifk, tofu, soybean sprouts, and soy sauce, and a variety of ingredients. such as soy flour, soy protein concentrates~ and is&&es, can be produced from soybean seeds. However, rather sophisticated processing procedures may have to be employed. For instance, the manufacture of tofu genera&+ requires several unit operat~ot~~~ cleaning, soaking, wet grinding, cooking, filtering. curdfing with calcium sulfate, filtering, pressing, and washing. Each unit process creates a waste problem, and for precipitation of curd, it atso introduces calcium suffate into the system. The use of this compound probably cannot be tolerated because of recycling compiic~tio~~s I?!. A recyclable substitute, such as vinegar, however, could be used. Soybeans could also be harvested at an early maturity stage as a vegetable.
t iR)244
H. Fuecd
Peanuts have high ~a~atab~~jt~ and can be consumed in a variety af forms or as an ~ngredjent for many food pr~paratioi~s~ Cowpea is not an oilseed, but consists mainly o~~arbobyd~ates and proteins; a variety of products can be formuiat~d from them. Cawpeas are grown for their seeds, pods, and/or leaves, which are consumed as green vegetables. Similar to the cereal crops, utilization or treatment of the non-edible portions of the legume crops is also very important to the realization of a CELSS. Raw oilseeds andior legumes could contain a significant amount of ~~ti~~trients or natural toxicants, such as protease i~~hibito~s, phytates, Iectins, etc. Peanuts may also be contamjnated with aflatoxin if not property stored. The main concern witb rapeseed is that it contains si~ni~cant amounts oferucic acid alld ~~u~os~i~o~~tes. which must be reduced to a very low level for hu;~a~ consumption. Most of the a~tin~l~rients or natural toxic substances in aitseeds andior legumes can be reduced by proper heating. S~aki~~~ plus cooking, ~ontr~~~~d germinations fermentations as well as e~~~~matic treatment may also be employed 171_ Other ~i~l~itatiol~sto the use of legumes (saybean and cowpoa) in food are the presence of a beany flavor and nondigestible carbohydrates, such as raffinose and stachyose, and lack of structural qualities. The beany flavor and nondigestible carbohydrates can be reduced or removed with proper processing methods, Legume flours are often mixed with wheat flour to improve nutritional quality of the composite without causing structural problems. An ~ptit~~lrn ratio of the composite fluur for a specific ~~ppli~atioi~ can be d~termjned by a mixture exper~me~~t. While afld Sweet Potatoes Both white potato and sweet potato contain high arno~~~~t~of d~gest~b~~ starch and low amulets of protein. Their fiber content is low but has good ~h~siolo~~~~l citara~t~ristics, and they are also good sources of vitamins and minerals. Their proteins include afI essential amino acids, with metl?jun~ne and cystine being somewhat fimitil?g for human nutritional requirements. E)oth white potato and sweet potato contain same antinutrients or toxic substances. Toxic proteinase inhibitors do not occur in significant concentrations. The main concern is the toxic &co-alkaloids, such as solanine in white potatoes, which occur during improper storage and are not heat-labile. It is important to select how-a~kaioid cultivars, and to grow and store the tubers under ~~ndjt~o~s that do not favor s&mine d~v~lopi~~en~. It is best to store in a coot, dry+ dark area, as g~er~~n~ in respanse to light takes place more rapjdl~ at room te~~~e~at~~e than irt a coo1 area. Sweet potatoes can be stored at room ternpe~t~r~ with low ~lu~~id~t~. Both white and sweet potatoes are fairly palatabie in their various forms of usage, They can be cooked, boiled, baked, fried, etc. They can also be ~~~~rporat~d into various food systems, such as bread, cake, cookies, and the like. The stems and leaves of sweet potatoes are edible while tbc foliage of white potatoes co~t~i1~~ poisanous alkaloids. ADAPTABILITY
OF FOOD TECHNOLOGY
TO SPACE ENVIRONMENT
Space conditions such as low gravity level, freezing temperatures, and thin or no atmosphere may influence fluid behavior, heat and mass transfer, as well as microbiai behavior /9/. Among them, gravity level appears to be the most s~~n~~~~antspace factor to ir&uence food processing. There are two different situations: one is the m~~r~&rav~ty that occurs in a free”~rb~ting space station; and the other is l~ypo~ravity, which occurs at the lunar fca. l/6 xg} or ~a~~~~ surface (ca. f/3 xg). On Earth (1 xg), the present food processing industry is s~f~~ient~y advanced such that basic food ~omFonents can be processed into almost any type of food with reasonable cast. The Each-based food rnac~~jff~~ and processing equ~~rnen~ are designed to take advantage of gravity to conrroi orientation of fluids, gases, and solids. tn the design process, gravity is often taken for granted, i.e.. separating h&s from cotyledons by airflow, filling a can with food, pr~p~~i~~ dough for baking, etc. Can we perform these operations without the help of gravity? What will happen under hypogravity? These questions and challenges remain to be answered. Operating without the adv~~~ta~e of gravity requires that all transfer of liquids or soIids be accomplished by means of pressure from one ~oi~~a~ner to another. inertial forces, surface forces, and viscous forces may be aproned to matter to transport, position, or contra! rnot~n~l, Free ~onv~~~ion wiff be replaced by
tm245
ProcessmgCELSS Foods
forced convection, and density separation will be replaced by inertial separation. Materiais must be positively fed into the device. A41 heating will be done by forced convection, conduction or radiation, such as in a forced convection oven, microwave heating, or radio frequency heating. A b4ast refrjgerator/free2er shontd be used instead of a still-air refr~gerator/free~er. Under microgravity, very few food processes can be employed without significant modification. Extrusion and membrane separation may be considered as gravity-irlsensitive processes. Extrusion is capable of p~rfor~~~~~ga number of operations, including cooking, forming, texturizing and dehydrating materials, particularly those from grains, legumes and seeds. The extrusion process is a4so energy efficient since extruded products with proper packaging are usually shelf-stable and require no refrigeration during storage. Another advantage of particular importance to CELSS application is the lack of process effluents. The feasibility of process adaptation for CELSS application has been investigated /I Oi. Some of the results will be presented in the next section. Membrane separation may be used for water recovery, juice concentration, etc. However, under hypogravity, most of the current operations, such as flour lniiii~lg, baking of bread and screw pressing of oilseeds, can be adapted to the space ~ilvir{~~~t~~e~it with minor rn~~di~catiol~s. The main challenge is to collect processing parameters so that a space-compatible system can be designed.
reliable
data
for
An idea4 food processing snbsyste~~ of a CELSS will provide lnu4tifuIlctionalit and dupability. For instance, with the proper rnodi~~atio~l, an oven should not only be able to bake, but also to warm, incubate, fry, toast, dry, condition, and even perform steaming i4 Ii. Similar ~oi~so4jdations can be made with cutting. slicing. and dicing, and with operations such as shredd~ng~ rasping, and grating. Much more research is needed on desigr~j~~g, ~~lodifyjl~g, ~onsoljdat~~~g or selecting spare-compatible equipment and utensils for food processing and preparatjon. Factors such as processing frequency, c~nsuinption rate, storage area, and the like need to be considered. Some space cotlditiolls/resources such as solar energy, few teI~~peratures and a thin atmosphere may be utifized for future food processing in space 191. The sold night temperature will permit cooling of many systems without the use of cryogenics. The constant freezing temperatilres below the lunar or Martian surface may be used as a naturaf freezer. For example, fresh pasta made by extrusion is mixed with tomato sauce. and frozen. ft can be heated by microwave for &oi~snlnptiol~. Both low temperature and vactmm or thin atmosphere may be bene~i~ia4 for some processes, such as vacuum drying and freeze-drying. A freeze-drying process sinlulating space atmospheric conditions has been developed /lY, which will also be discussed later. During lunar days, high temperature and vacuum my allow better solar drying of some materials (e.g. potato) with less oxidation.
The main purpose of extrusion is to increase the variety of foods in the diet, by producing a range of products with different shapes. textures. colors, and flavors from basic ingredients. Pasta is targeted for prodn~tioll in a CELSS as part of a strict vegetarjaI1 diet or if some meat is col~sumed. Pasta has the positive attributes of versatility. convenience, economics, taste, and nntrit~on” Cowpea amino acids comp4ement cerea4 proteins since iegumes are limited in su4fur-containing amino acids and cereals are limited in iysine. The objective of the study was to produce an extruded pasta with i~nProved protein content and amino acid profile by pa~ially substituting whole cowpea mea4 for durum wheat semolina.
California ii5 biack eyed peas were ground into a coarse meai, mixed with ConAgra if4 semolina in various &~inbiIlatjons in the ratios of 0: IOO, ‘t&%I, 20:80, 3270, and 40~30. The mixtures were b4el~ded with 2% ~~ol~og4y~eride powder, which functions as an extrusion aid. Water was added to bring the mixture ta 33% moisture. Mixtures of O-40% cowpea with semolina were extruded on a Brabender single-screw extruder equipped under conditions of low shear (27 RPM) and moderate temperature (50 o C) that do not cook the product. The extruder was allowed to pre-heat for 5 min. Once heated, the screw was fed for IO min prior to data and sample collection. Protein quality, sensory acceptability, raw pasta
(l/2)246
H.
color, cooking evaluated.
FuPI01
loss and water uptake as well as energy consumption
in each unit operation
were
Results and Discussion The protein content of durum semolina pasta was improved by addition of cowpea. An increase in protein content would be expected by the supplementation of wheat semolina (16% protein, dwb) with cowpea meal (26% protein, dwb). Protein quality can be estimated from the amino acid profile and invitro digestibility. By combining wheat and cowpea, the limiting essential amino acids are provided in greater quantities to yield a more balanced essential amino acid profile. One serving of 10% cowpea pasta could theoretically provide approximately 32% of the USRDA for both lysine and sulfurcontaining amino acids. However, the addition of cowpea to semolina did not significantly affect the invitro digestibility of pasta. Raw semolina pasta exhibited similar digestibility to that of raw semolina, indicating a lack of protein quality improvement by the extrusion process under these processing conditions (27 RPM. 50 “C). Boiling of the pasta slightly improved the digestibility of semolina pasta. Inactivation of heat-labile antinutrients could contribute to the improvement of protein quality. In general. sensory quality tends to decline when traditional food products are substituted with legumes to improve the nutritional quality. Consumer acceptance of a food is based upon the perception of flavor, color. and texture. and their own personal prejudices. Of the variations evaluated. the lowest level of cowpea substitution produced the most acceptable product (Table 3). Sensory scores for the 10% cowpea pasta were not significantly different from the durum control in the areas of flavor, color and overall quality. Flavor scores of the 20% cowpea pasta were not significantly different from the 10% version but were different from the control. This implied that a level of substitution between 10 and 20% would also produce a pasta with acceptable flavor. The beany flavor cited in the 30-40% cowpea pasta could be reduced by inactivating lipoxygenase, which can be responsible for the off-flavor of legumes. In addition, early harvest of cowpeas may precede the deposit of antinutrients in the legume and reduce the need for rehydration during food processing. Color and flavor scores displayed the same trend in panelist acceptance. No significant differences were found for these characteristics between the control and 10% cowpea pasta. Texture scores for cowpea pasta, however. were affected by the level of substitution. All levels studied produced scores significantly different from the durum control. Objective indices were not significantly affected the cowpea pasta were within the maximum limit slightly by substitution. However, the color of Lightness and yellowness for 30 and 40% cowpea of substitution.
at low level of cowpea substitution. Cooking losses of of 9% set by industry /lo/. Water uptake was affected by the addition of cowpea. pasta was influenced meal were significantly different from the lower levels
The addition of cowpea also affected dough behavior during extrusion. With process parameters fixed, it was shown that cowpea reduced the pressure drop and product flow rates. Cowpea increased the dough stickiness so significantly that an extrusion aid--monoglyceride, had to be incorporated. Reformulation or optimizing process parameters may be an alternative to this aid. TABLE 3 Means comparison of sensory scores for durum semolina pasta and durum semolina pasta substituted with cowpea * Texture
quality
Flavor
0.64 a
0.54 a
20 30
3.12 a 5.78 b 9.03 bc
3.13 ab 5.07 b 8.21 c
I .53 a 5.92 b 6.94 bc 8.14 cd
4.70 a 5.06 b 7.28 bc
40
10.43 c
9.92 c
IO.28 d
8.15 c
IO
a, b, c, d Means with the same letter in the same column (~~0.05). Data are from Kanach /I Oi. * where
Overall
Color
Cowpea level (‘%J) 0
2.89 a
were not significantly
different
The energy and manpower requirements for the process were estimated and are presented in Table 4. It is noted that the electric ~eqnireInent for extrusion was much higher than the average value of commercial processes, which is about ML 4 - Cl.2 kW l&g product 1131.One of the reasons could be due to the small experimental state. Further ~nvest~gatj~~~ is needed to verify the inforl~at~ot~.
Potato slices were chosen as a mode! food system fo ~re~e-~~. White potatoes, c&ivar Russet ~~rk~ta~~,c~~~ta~~~~n~ about 82% moisture were cut into 6.3 mm slices, jndiv~~~a~~~quick frozen. and stored at -40 ‘YI. A ~~~trogenat~nos~~~erewas used at the lowest prcssurc 267 Pa achieved by the freeze dryer to a~~r~~c~ conditions on the Moon, Carbon dioxide ~~ainta~nedat 773 Pa was used to simulate a Martian atmosphere. A Labconco freeze dryer with a heat rack was modified by attaching a gas inlet valve to a port on the drying chamber. For each observation, approximately 100 g of potatoes were accurately weighed and placed on the heat rack in the drying chamber. The chamber was evacuated, filled with the desired gas (nitrogen or carbon dioxide), and evacuated again, insuring that the drying occurred in the desired atmosphere. The pressure level of the simulated at~~ospl?~~ein the chamber was ~~onitored by a millitorr meter. For observations at 173 Pa, the gas valve was sl~~~t~~opened tn allow the chamber to ~~~ai~~tajn the required pressure. For observations at the higher plate temperature (33”C), heat pfzz&eswere first turned or? two hours after drying began to prevent melting and collapse of the product. After the specified drying time, the vacuum was broken with the desired gas. The slices were removed and weighed to crilculare the remaining moisture content.
Free~e-dryillg isa viable aption frtrfcmf~rese~a~jan in a Lmar or Ma~ja~ QU~FQS~~F~g~~~I ~~~~~~6~ moisture ioss of potato slices during ~ree~e-dr~~n~at 20°C. The cririca! moisture co~~e?~tfor dried ~~~aF~ sks is about 3%. The optii~~m drying time for potato siices in a ~arbu~ dioxide at~~~~~~l~~e at XP@ is about 12 h. Tbe o~~~rn~rndry~~gtime in nitrogen is about 15 h. The difference could be due to the higher thermat co~ducti~jty in the presence of CO2 than I?2 or could be due to the v~r~ab~~ity of thermal conductivity fram one sample to another. Figure f also shows that the higher at~~os~heric pressure results iu a siower dryiug process since the higher pressure causes a smaller pressure gradient, which is the d~ivj~g force for mass transfer during ~~~~~e-d~~~g. Using heat&g plates at 43°C greatly reduced the ~~~i~~~Gne at 267 Pa. However, heating at 43Y Ied to ~~e~ti~~g for both a carbon dioxide and a i~jtro~~~atmosphere of 733 Pa. A small amount o~bro~~~~~gon the surface was observed from the
( 1111248
.
_____
267 Pa
CO2
773 Pa
CO2
267 Pa
N2
773 Pa N2 __. ..
Freezing time (hr)
Fig. I. Freeze~dryitl~ curves ofpotato slices in simuIated space conditions with the heating plate temperature of’ 20 OC ll~j~-b~a~c~ed potato slices. ‘This could be either enzymatic or f~~~~~e~l~~~l?atic or both. Further work is being undertaken to study the effect of freeze-drying on food quality under simulated space conditions. Product characteristics. such as vitamin C content. color. pi-f, texture. and rehydrat~on ratio are being studied.
Oil is the most coI~~e]~trated form of ef~ergy-produ~ii~g nutrients. Oil may be used directly in food preparation or as an iI~gredi~]~t in food products made from CELSS crops. Oil extractjon is an i~npot~a~~t step for utilizing oilseeds. The current commercial process to extract oil is not suitable for the CELSS e~?viro~~I~e~~tsince it involves a flammable organic solvent, hexane. Mechanical extraction of oil normally involves a ~ornbiilatiol~ of seed preparation and heating and expelling processes, Processir~g col~ditiolls will he d~c~ted by oil quality and protein quality of the press cake as well as e~trac~io1~ efficiency. The col~rnoi~ly recognized disadvantage of tow extraction ef~ciellcy may not be a problem for a CELSS sincethe press cake will be further processed for human consumption and will be as important as the oil. Characteristics of the low-fat cake from oil pressing need to be studied, and its utilization in various food systems needs to be investigated. New alternative food processing methods or novel CojnbiI~atiol~s of existing methods are ~;~~~~jnuall~ being illvesti~ated in the pursuit of producing better quality foods more e~onorni~ali~. S~lper~ritical fluid extraction is sucl~ a process that may also be used to extract oil from oiiseeds /‘I 9, An important feature in favor of supercritical extraction is the possibility of using a ilo~~~a~~~tnabi~ and innocuous medium. forexaI~pie CO2. At pressures above 30 MPa and at telnperat~lr~s between 60 and WC, seed oils are fairly soluble in compressed COz. The dissolved oil is free from pllosphatid~s. This process can be combined with the mechanical oil pressing discussed above. The residual oii in the resultant press could be treated with supercritical CO2 as a further procedure. ~esoivei~ti~~ is urmecessary because the compressed gas rapidly escapes from the cake once processing has ended. Carbon dioxide under pressure can also kill bacteria, molds, and yeasts. The effect could be s~ll~rgisti~ with raised temperature and acidic pH and antagoll~ed by lowered water activity.
PmesstngCEL.S Foe&
f1/2Y%49
High hydrostatic pressure is another new process that may be used to inactivate microorganisms in certain foods or food ingrediel~ts /I&‘. The appJi~ation of hydrostatic pressure is uniform and i~~stantaneoustl~rougho~~ta food. It is unique in that the effects do not fotlow a concentration gradient. A ~ornbinatjol~ with other metilods may be necessary since most bacteriaf spores are scarcely affected by pressure and enzymes are also quite resistant. They may have to be inactivated by heat. Nowever, different foods react differently to pressure in their flavor, texture, and color responses with ~~rr~s~oi~djn~Jy different storage effects, The type of foods most likely to benefjt from this novel processing. especially in the CELSS ~~~viro~rnent~remain to be jdentj~ed and deveioped. This te~J~~~~Jo~~ may aEso End a~~~j~at~onin other subsystems~ such as waste ~~atrne~t ~su~er~rjt~~aiwater oxidation), and plant growth (sterilization of nutrient medium). T~~bnoJogy advances are needed before it can actmlly be utilized. An aqueous extraction method may be employed as an alternative oilseed milling process to extract oil, protein and starch sit~~ulta~le~usl~1171.Ohmic heating, osmotic drying, and modified and controlled atmosphere J~a~kagil~~may also be emptoyed for CELSS purposes. However, more research is definitely needed to identify the type of foods that can benefit from these processes in the CELSS environment.
How to produce nutritious, safe, pala~abJe. and versatile foods from a limited source of bjo~~ss materi&, with serious ~o~lstraiilts in space and facilities for food processing and ~re~aratjoll, will continue to challenge food scientislsiengineers. Research efforts are needed at least in the folJow~~~g areas: (1) Further j~lvestigatiol~of adaptability of ~o~~~~F~o~~~ food ~rocessjfl~ operations to the space el~vir~~ilrn~nt~ (2) developmei~t of novel gravity-il~sellsitive professing systems; (3) potential appii~ations of space resources; (4) utilizations of I~oIl-traditional plant biomass or food sources for both food or nonfood purposes. which ~311play 3 key roie in reducing the Joad for recpcting and regeneration in 3 CEIS. For esamplc, food ~l~~redi~l~ts such as glucose and vinegar, may be ohtamed from waste recovery, which may be used in n~al~u~~ct~~rj~~~ engineered foods or other food products. Progress in otJ%erareas, such as plant ~~~du~tjo~?,genetic e~~~i~~eerin~, waste Trident, and autol~atjo~~ may also impact the design of the food processing s~lbsystem for a CELSS Some plant ~hara~ter~stj~s~ such as harvest index and piant ~o~~pos~t~o~~, can be jm~roved by geer-retkl~odj~~atjo~?or o~t~rn~~atjol~ of growing conditions, For example. a dwarf eanoJa rapeseed is being d~~eJoped by genetic et~g~~e~rii~~ 1%. If the urucic and gJ~~osil~atescan be reduced suf~ci~~ltl~~,then both the oil aud the cake could be used far human co~lsu~n~tioI1directly without any addit~oI~a~processing steps. Another example would he to genetically remove the liposygenase, which is responsible for the beany tlavor in many bean products /IX/. This will not only improve the quality but may also lessen the processing requirements. ‘The de~el~~~~~~~~~t of ~~~teJli~e?~t robots wilt de~n~teJ~ liberate l~urna~sand ill~lue~~~ethe design of food processing hardware. In additjo~~,~o~lt~~~~~s~~ research on human phys~oio~~~aJresponses to the Jobs-term space ~~~~;i~~~~~~i~~ will certainly lead to better und~rstandin~ of human I~utr~t~onaJ reqn~r~~~e~~s.thus jn~~u~~~cjl?~ meal pre~arat~ol?.There is much to be done before food ~roc~ssin~ can occur Jn space.
3. SM. Schwartzkopl%, Design of a controhed ecological life support system, ~~~~,~~~~~~g. Q (7). 526-535 {1992). 4. i& KareJ and AR. Kamare~, ~easjb~~~tyof~rodu~~~?ga range of food products from a Jii~~~edrange of ~~~d~ffereI~tiated major food ~~rnp#~~~ts~ NASA CR- I77329, I t 984).
8. Fu et al.
(In)zFo
5. M. Karei and Z. Nakhost, Utilization of non-conventional components, NASA CR-I 77545, (1989).
systems for conversion
6. Z. Nakhost and M. Karel, Utilization of non-conventional components. NASA CR- 177449, (I 986).
systems for conversion
of biomass to
food
of biomass to food
7. J.E. Hoff, J.M. Jowe, and CA. Mitchell, Nutritional and cultural aspects of plant species selection for a regenerative life support system, NASA CR-1 66324, (I 9X2). 8. HR. Takruri, M.A. Humeid, and M.A.W. Umari, Protein quality of parched immature Sci. Fmd Agr.. 50, 3 19-327 (I 990). 9. I3. Fu and P.E. Nelson, Conditions
and constraints
offood
durum wheat, J.
processing in space. Food ~~~~~~~~~, (in
print). 10. L.L. Kanach.
Extrusion
of Durum Semolina
M.S. thesis, Purdue University,
W. Lafayette,
Substituted with Cowpea and Assessment of Quality,
IN. (1993)
I 1. T. Parks, An approach to the development of equipment design concepts for processing food and biomass aboard a space station or lunar module, NSCORT seminar. December 3, Purdue University, W. Lafayette,
IN. f 199 I ).
12. R. Irvine, K. Cooksey, and FE. Nelson, Feasibility of freeze dellydration under lunar and Maniacs conditions, presentated at the Institute of Food Technologists Annual Meeting, June 25-29, Atlanta, GE. (1994). 13. J.M. Harper. Food extrusion,
L’uit.Rev. FoociSci. Ah@%,JJ., 155-215 (19791,
14. D.M. Bird, G.E. Seely. C.L. Miller, D.E. Sandlin, M.R. Yakely, A.C. Gomillion. and P.J. Holland, Harnessing the resources space in the recovery of potable water from waste water by Iyophilization, 23rd International Conference on Environmental Systems, Colorado Springs, CO. ( 1993).
of
16. R, Eggers and U. Sievers, Processing of oilseed with supercriti~al Jupun, a
carbon dioxide,
f. ~~~~. EBB
(6). 64 I-649 f i 989).
17. C. M. Carter, K.C. Rhee. R.D. Hageilmaier, and K.F. Mattil, Aqueous ~xtractioll-an process, JAOC??.5.J_,137-141(1974).
alternative
oilseed milling
18.C.S. IJavies, S.S. Nielsen, and N.C. Nielsen, Flavor improvement 64(IO), 1428-1433 (1987). of liposygenase--, 3 s/4oc-s, .
ofsoybean preparations
by genetic
removal
Journal Series Paper No. 14345 from the Purdue Unjversity is partially supported by NASA grant NAGW-~~29-
Agricultural
experiment
Station. This work
Pergamon
0273- 1I77(95)008 W-4
PROCESSING OF N~~~T~OUS, SAFE AND ACCE~A~LE FOODS FROM CELSS CANDIDATE CROPS B. Fu, P. E. Nelson, R. Irvine and L. L. Kanach
ABSTRACT A controlled ecological life-support system (CELSS) is required to sustain life for long-duration space missions, The challenge is preparing a wide variety of tasty, familiar, and nutritious foods from CELSS candidate crops under space environmental conditions. Conventional food processing technologies will have to be modified to adapt to the space ei~vironment. Extrusion is one of the processes being examined as a means of converting raw plant biomass into familiar foods. A nutrition-improved pasta has been developed using cowpea as a replacement for a portion of the durum semolina. A freeze-drying system that simulates the space conditions has also been developed. Other technologies that would fulfill the requiremeilts of a CELSS will also be addressed. INTRODUCTION The development of space food has evolved from tubes and cubes to near Earth-like cuisine over the past 30 years it/, On current missions, spacecraft crews consume foods stored aboard their spacecraft. As the i~uman presence in space increases in duration, in numbers of people, and in distance from Earth, the economics of resupply and sizing of space habitats for storage of life-support items (including food) become major limiting factors. Extraterrestrial and in-flight food processing and packaging become necessary when edible biomass is to be produced in situ. At Purdue University’s NASA Specialized Center of Research and TraiIling ESCORTS in bioregenerative iife-suppo~, pllotosyllt~leti~ plant crops are proposed to be the primary candidates for biomass production in a controlled ecological life-suppo~ system (CELSS) 121, based on the fact that people on Earth can live on pure vegetarian diets, Plant species growing in a CELSS must provide a nutritionaIly and psychologically adequate diet for human il~habitaitts living on the moons free-space se~lements, or other planets. Alternative biological systems (aquatic species, algae, and mushrooms) may also play a role in a future CELSS, especially for protein production and waste conversion /3/. One of the basic requirements for food processing is to make the foods taste good. Military experiences have shown that troops will not necessarily eat “enough of anytIling” when they are hungry if the food does not taste good or if they are tired of the food. Nutrients are of no value unless consumed. One can not meet the demand by just serving up parts of the candidate crops. The key lies in the utilization of somewhat more complex processes within the overall technological and engineering constraints of the CELSS {Table 1) to produce diversity of products that increase palatability and provide useful functional properties. Other basic requirements and operation requirements for food processing are also listed in Table 1. So far, most effort has been directed to more efftcient biomass production, and less work has been done on the conversion of traditionaily non-edible plant biomass into foods. Karet and Kamarei 141 investigated the feasibiiity of producing a range of engineered or fabricated foods from a limited range of utldifferentiated major food components. The question is how to develop spacecompatible food fabrication processes. In another study, Karel and Nakhost /S/6/ isolated high quality proteins from green algae and incorporated them into several foods, such as muffins and fettuccine. Organoleptic acceptability of these so-called “novel products” made from nontraditional food sources, however, has been a major challenge. Achieving acceptance continues to challenge food scientists and technologists.
w2)241
(l/2)242
H. Fu el al.
TABLE 1 Requirements
and constraints
of food processing
in space
1 Constraints Space environment Hardware weight and volume Power Crew time Unconventional biomass Plant toxicants/antinutrients Volatiles and chemicals Dust and particulates ~icroorganisIns Packaging materials 1 Waste disposal
Requirements Safe Nutrjtjous Palatable Versatile Familiar Storage stability Easy to prepare Easy to operate Easy to clean-up Reliable and flexible Clean-room processing
Our objective is to develop a space-compatible system that can produce safe, nutritious and palatable foods from CELSS candidate crops. In this paper, processing characteristics of the CELSS candidate crops and adaptability of conventional food processing technologies to the space environment will first be discussed. Results from two case studies, extrusion of cowpea-substituted pasta and freeze-drying of potatoes under simulated space atmospheric conditions, will be presented. Finally, some potential technologies with possible applications in a CELSS will be addressed briefly. PROCESSING
CHARACTERISTICS
OF CELSS CANDIDATE
CROPS
Some CELSS candidate crops and their characteristics are listed in Table 2. These species are selected mainly based upon criteria such as nutritional quality, versatility of food products they can produce, as well as the amount of processing necessary to render the products edible /7/. Lettuce. Tomato and Radish Lettuce, tomato, and radish are considered salad crops. They are good sources of vitamins and minerals. When eaten raw, all three are considered detergent foods, important to dental health. Tomato is also a standard item in soup and the base for many delightful sauces and dressings. It can be eaten fresh or can be cooked in many forms: stewed, fried, and baked. These materials are not considered protein sources and usually do not contain significant amount of antinutrients or natural toxicants. Both lettuce and radish should be stored under refrigeration with very high humidity. Tomatoes should not be refrigerated until such time as they are fully ripened. The tomato plant has much less edible portion that do the other two crops since its stems, leaves and roots are inedible. That is, tomato has a relatively low harvest index (fraction of total biomass that is edible). Rice and Wheat The major col~stituent of cereal grains is starch. Rice contains considerably less protein than wheat, but its protein has a somewhat higher biological value. These proteins are deficient in lysine and tryptopllail. The vitamin and lipid contents depend upon the degree of refining, and cereal grains contain antinutrients, such as phytates and protease inhibitors, that could become significant if not properly processed. Cereal crops in general have a low harvest index. Thus, utilization or treatment of the nonedible materials is critical to the success of a CELSS. The type and quality of products obtained from cereal grains depend on the type and quality of the grain used and its processing. Rice grains are often consumed as whole kernel rice after some type of milling. Rice can also be used for flour or baked goods, but wheat is probably the most versatile of the grain crops as a food. The wheat protein (gluten) has unique elastic and gas retention properties, which are responsible for the ability of wheat to form leavened products and extruded pasta products. It can be processed and served in numerous forms and combinations. Various degrees of refining are required to take full advantage of this crop; however, the degree of refining is constrained by the CELSS
Prcxx=sing
t 112t241
C‘ELSS Foodr
TABLE 2 CELSS candidate crops and their char~cterjstjcs~ CEXpS
Lettuce Tomato Radish Rice Wheat
Main nutrients Fiber, VA, VC, Fe, Ca VC, VA, K, P VC, K, Mg CHO, protein, VBs, MS CHO, protein, VBs, MS Lipid, Protein, CHO
Deficients
~ntin~t~~e~~/toxic~~ts
Main uses
Nitrates Glucasinates Phytates
Salad Salad, juice, sauce Salad, cooking Cooking
Phytates, PI
Bread, pasta
Qif. soymitk tofu, TX phytates, fecfins, saponins, tlatulussoysauce producing ol~gos~cci~arid~s A~ato~i~~s~ Pf . phytates, Oil, roasting, peanut Lipid. protein, CHO Peanut lectins bntter Erucic acid, g~ueosjnat~~ Oif Rapeseed Lipid phytates, goitrogens Phytates. &tins, PI, Leaves for salad. CHO, protein, fiber COWQtXk seed for cooking ~atulus~p~odLicing oligos~ccharides Solanines, lectins, Pf Cooking. baking ct-ra,vc. VBS. Fe, P P~~~to~~~~jns, P1 Sweet paato CHO, VA, VC, MS Met Baking * VA-~~tal~~~l A: VC-vitamin C; VBs-vitamins B; &%+-minerals; CHU~ar~ollj~~drates~ Lys---fysine: Try-tr~ptop~~an~ Cys-cysteine; Thr-threine: Met-methinne; Pf-protease inhibitors
Soybean
environmel~t. Bran and germ disp~s~~/~tili~ation is also an issue. Recently, it becomes common for some people to use whole wheat flour in making bread or other similar products. The tbrcshed whole wheat grains can also be consumzd after parboiling.
of dwmn wheat was found to be higher tvhen harvested at an ear1.v stage of maturity compared to a later stage of maturity or at fulif maturity iii/‘. This finding suggests that further i~lvcsti~atioi~ into the functioI~a~ and ~~utritiona~ advantages of early-harvest wheat could be beneficial to CELSS from more than just a growth-cycle standpoint.
The pm&in ef~~je13cy rario(PER)
Soybean. Peamn, Rapeseed and Cowneg! Soybean peanut. and rapeseed are oiiseeds, They mainly provide lipid, protein3 and car~o~~d~~~~ in the edibie portion. Their prot&s ~~~~ra~~~ are rich ia Ipine but tack s~~f~~-co~~~a~~~~~~ amino acids. OII can be extracted from the oilseeds mecI~a~~~cal~yand is suitable for consu~~pt~or~ as a salad oii, frying medium, bakery ingredient, or many other uses. Fortunately, the soiid residues from the extraction process can be further processed for human consumption. Different Jevels of processing may be involved depending on the final products desired. A variety of products, such as soymifk, tofu, soybean sprouts, and soy sauce, and a variety of ingredients. such as soy flour, soy protein concentrates~ and is&&es, can be produced from soybean seeds. However, rather sophisticated processing procedures may have to be employed. For instance, the manufacture of tofu genera&+ requires several unit operat~ot~~~ cleaning, soaking, wet grinding, cooking, filtering. curdfing with calcium sulfate, filtering, pressing, and washing. Each unit process creates a waste problem, and for precipitation of curd, it atso introduces calcium suffate into the system. The use of this compound probably cannot be tolerated because of recycling compiic~tio~~s I?!. A recyclable substitute, such as vinegar, however, could be used. Soybeans could also be harvested at an early maturity stage as a vegetable.
t iR)244
H. Fuecd
Peanuts have high ~a~atab~~jt~ and can be consumed in a variety af forms or as an ~ngredjent for many food pr~paratioi~s~ Cowpea is not an oilseed, but consists mainly o~~arbobyd~ates and proteins; a variety of products can be formuiat~d from them. Cawpeas are grown for their seeds, pods, and/or leaves, which are consumed as green vegetables. Similar to the cereal crops, utilization or treatment of the non-edible portions of the legume crops is also very important to the realization of a CELSS. Raw oilseeds andior legumes could contain a significant amount of ~~ti~~trients or natural toxicants, such as protease i~~hibito~s, phytates, Iectins, etc. Peanuts may also be contamjnated with aflatoxin if not property stored. The main concern witb rapeseed is that it contains si~ni~cant amounts oferucic acid alld ~~u~os~i~o~~tes. which must be reduced to a very low level for hu;~a~ consumption. Most of the a~tin~l~rients or natural toxic substances in aitseeds andior legumes can be reduced by proper heating. S~aki~~~ plus cooking, ~ontr~~~~d germinations fermentations as well as e~~~~matic treatment may also be employed 171_ Other ~i~l~itatiol~sto the use of legumes (saybean and cowpoa) in food are the presence of a beany flavor and nondigestible carbohydrates, such as raffinose and stachyose, and lack of structural qualities. The beany flavor and nondigestible carbohydrates can be reduced or removed with proper processing methods, Legume flours are often mixed with wheat flour to improve nutritional quality of the composite without causing structural problems. An ~ptit~~lrn ratio of the composite fluur for a specific ~~ppli~atioi~ can be d~termjned by a mixture exper~me~~t. While afld Sweet Potatoes Both white potato and sweet potato contain high arno~~~~t~of d~gest~b~~ starch and low amulets of protein. Their fiber content is low but has good ~h~siolo~~~~l citara~t~ristics, and they are also good sources of vitamins and minerals. Their proteins include afI essential amino acids, with metl?jun~ne and cystine being somewhat fimitil?g for human nutritional requirements. E)oth white potato and sweet potato contain same antinutrients or toxic substances. Toxic proteinase inhibitors do not occur in significant concentrations. The main concern is the toxic &co-alkaloids, such as solanine in white potatoes, which occur during improper storage and are not heat-labile. It is important to select how-a~kaioid cultivars, and to grow and store the tubers under ~~ndjt~o~s that do not favor s&mine d~v~lopi~~en~. It is best to store in a coot, dry+ dark area, as g~er~~n~ in respanse to light takes place more rapjdl~ at room te~~~e~at~~e than irt a coo1 area. Sweet potatoes can be stored at room ternpe~t~r~ with low ~lu~~id~t~. Both white and sweet potatoes are fairly palatabie in their various forms of usage, They can be cooked, boiled, baked, fried, etc. They can also be ~~~~rporat~d into various food systems, such as bread, cake, cookies, and the like. The stems and leaves of sweet potatoes are edible while tbc foliage of white potatoes co~t~i1~~ poisanous alkaloids. ADAPTABILITY
OF FOOD TECHNOLOGY
TO SPACE ENVIRONMENT
Space conditions such as low gravity level, freezing temperatures, and thin or no atmosphere may influence fluid behavior, heat and mass transfer, as well as microbiai behavior /9/. Among them, gravity level appears to be the most s~~n~~~~antspace factor to ir&uence food processing. There are two different situations: one is the m~~r~&rav~ty that occurs in a free”~rb~ting space station; and the other is l~ypo~ravity, which occurs at the lunar fca. l/6 xg} or ~a~~~~ surface (ca. f/3 xg). On Earth (1 xg), the present food processing industry is s~f~~ient~y advanced such that basic food ~omFonents can be processed into almost any type of food with reasonable cast. The Each-based food rnac~~jff~~ and processing equ~~rnen~ are designed to take advantage of gravity to conrroi orientation of fluids, gases, and solids. tn the design process, gravity is often taken for granted, i.e.. separating h&s from cotyledons by airflow, filling a can with food, pr~p~~i~~ dough for baking, etc. Can we perform these operations without the help of gravity? What will happen under hypogravity? These questions and challenges remain to be answered. Operating without the adv~~~ta~e of gravity requires that all transfer of liquids or soIids be accomplished by means of pressure from one ~oi~~a~ner to another. inertial forces, surface forces, and viscous forces may be aproned to matter to transport, position, or contra! rnot~n~l, Free ~onv~~~ion wiff be replaced by
tm245
ProcessmgCELSS Foods
forced convection, and density separation will be replaced by inertial separation. Materiais must be positively fed into the device. A41 heating will be done by forced convection, conduction or radiation, such as in a forced convection oven, microwave heating, or radio frequency heating. A b4ast refrjgerator/free2er shontd be used instead of a still-air refr~gerator/free~er. Under microgravity, very few food processes can be employed without significant modification. Extrusion and membrane separation may be considered as gravity-irlsensitive processes. Extrusion is capable of p~rfor~~~~~ga number of operations, including cooking, forming, texturizing and dehydrating materials, particularly those from grains, legumes and seeds. The extrusion process is a4so energy efficient since extruded products with proper packaging are usually shelf-stable and require no refrigeration during storage. Another advantage of particular importance to CELSS application is the lack of process effluents. The feasibility of process adaptation for CELSS application has been investigated /I Oi. Some of the results will be presented in the next section. Membrane separation may be used for water recovery, juice concentration, etc. However, under hypogravity, most of the current operations, such as flour lniiii~lg, baking of bread and screw pressing of oilseeds, can be adapted to the space ~ilvir{~~~t~~e~it with minor rn~~di~catiol~s. The main challenge is to collect processing parameters so that a space-compatible system can be designed.
reliable
data
for
An idea4 food processing snbsyste~~ of a CELSS will provide lnu4tifuIlctionalit and dupability. For instance, with the proper rnodi~~atio~l, an oven should not only be able to bake, but also to warm, incubate, fry, toast, dry, condition, and even perform steaming i4 Ii. Similar ~oi~so4jdations can be made with cutting. slicing. and dicing, and with operations such as shredd~ng~ rasping, and grating. Much more research is needed on desigr~j~~g, ~~lodifyjl~g, ~onsoljdat~~~g or selecting spare-compatible equipment and utensils for food processing and preparatjon. Factors such as processing frequency, c~nsuinption rate, storage area, and the like need to be considered. Some space cotlditiolls/resources such as solar energy, few teI~~peratures and a thin atmosphere may be utifized for future food processing in space 191. The sold night temperature will permit cooling of many systems without the use of cryogenics. The constant freezing temperatilres below the lunar or Martian surface may be used as a naturaf freezer. For example, fresh pasta made by extrusion is mixed with tomato sauce. and frozen. ft can be heated by microwave for &oi~snlnptiol~. Both low temperature and vactmm or thin atmosphere may be bene~i~ia4 for some processes, such as vacuum drying and freeze-drying. A freeze-drying process sinlulating space atmospheric conditions has been developed /lY, which will also be discussed later. During lunar days, high temperature and vacuum my allow better solar drying of some materials (e.g. potato) with less oxidation.
The main purpose of extrusion is to increase the variety of foods in the diet, by producing a range of products with different shapes. textures. colors, and flavors from basic ingredients. Pasta is targeted for prodn~tioll in a CELSS as part of a strict vegetarjaI1 diet or if some meat is col~sumed. Pasta has the positive attributes of versatility. convenience, economics, taste, and nntrit~on” Cowpea amino acids comp4ement cerea4 proteins since iegumes are limited in su4fur-containing amino acids and cereals are limited in iysine. The objective of the study was to produce an extruded pasta with i~nProved protein content and amino acid profile by pa~ially substituting whole cowpea mea4 for durum wheat semolina.
California ii5 biack eyed peas were ground into a coarse meai, mixed with ConAgra if4 semolina in various &~inbiIlatjons in the ratios of 0: IOO, ‘t&%I, 20:80, 3270, and 40~30. The mixtures were b4el~ded with 2% ~~ol~og4y~eride powder, which functions as an extrusion aid. Water was added to bring the mixture ta 33% moisture. Mixtures of O-40% cowpea with semolina were extruded on a Brabender single-screw extruder equipped under conditions of low shear (27 RPM) and moderate temperature (50 o C) that do not cook the product. The extruder was allowed to pre-heat for 5 min. Once heated, the screw was fed for IO min prior to data and sample collection. Protein quality, sensory acceptability, raw pasta
(l/2)246
H.
color, cooking evaluated.
FuPI01
loss and water uptake as well as energy consumption
in each unit operation
were
Results and Discussion The protein content of durum semolina pasta was improved by addition of cowpea. An increase in protein content would be expected by the supplementation of wheat semolina (16% protein, dwb) with cowpea meal (26% protein, dwb). Protein quality can be estimated from the amino acid profile and invitro digestibility. By combining wheat and cowpea, the limiting essential amino acids are provided in greater quantities to yield a more balanced essential amino acid profile. One serving of 10% cowpea pasta could theoretically provide approximately 32% of the USRDA for both lysine and sulfurcontaining amino acids. However, the addition of cowpea to semolina did not significantly affect the invitro digestibility of pasta. Raw semolina pasta exhibited similar digestibility to that of raw semolina, indicating a lack of protein quality improvement by the extrusion process under these processing conditions (27 RPM. 50 “C). Boiling of the pasta slightly improved the digestibility of semolina pasta. Inactivation of heat-labile antinutrients could contribute to the improvement of protein quality. In general. sensory quality tends to decline when traditional food products are substituted with legumes to improve the nutritional quality. Consumer acceptance of a food is based upon the perception of flavor, color. and texture. and their own personal prejudices. Of the variations evaluated. the lowest level of cowpea substitution produced the most acceptable product (Table 3). Sensory scores for the 10% cowpea pasta were not significantly different from the durum control in the areas of flavor, color and overall quality. Flavor scores of the 20% cowpea pasta were not significantly different from the 10% version but were different from the control. This implied that a level of substitution between 10 and 20% would also produce a pasta with acceptable flavor. The beany flavor cited in the 30-40% cowpea pasta could be reduced by inactivating lipoxygenase, which can be responsible for the off-flavor of legumes. In addition, early harvest of cowpeas may precede the deposit of antinutrients in the legume and reduce the need for rehydration during food processing. Color and flavor scores displayed the same trend in panelist acceptance. No significant differences were found for these characteristics between the control and 10% cowpea pasta. Texture scores for cowpea pasta, however. were affected by the level of substitution. All levels studied produced scores significantly different from the durum control. Objective indices were not significantly affected the cowpea pasta were within the maximum limit slightly by substitution. However, the color of Lightness and yellowness for 30 and 40% cowpea of substitution.
at low level of cowpea substitution. Cooking losses of of 9% set by industry /lo/. Water uptake was affected by the addition of cowpea. pasta was influenced meal were significantly different from the lower levels
The addition of cowpea also affected dough behavior during extrusion. With process parameters fixed, it was shown that cowpea reduced the pressure drop and product flow rates. Cowpea increased the dough stickiness so significantly that an extrusion aid--monoglyceride, had to be incorporated. Reformulation or optimizing process parameters may be an alternative to this aid. TABLE 3 Means comparison of sensory scores for durum semolina pasta and durum semolina pasta substituted with cowpea * Texture
quality
Flavor
0.64 a
0.54 a
20 30
3.12 a 5.78 b 9.03 bc
3.13 ab 5.07 b 8.21 c
I .53 a 5.92 b 6.94 bc 8.14 cd
4.70 a 5.06 b 7.28 bc
40
10.43 c
9.92 c
IO.28 d
8.15 c
IO
a, b, c, d Means with the same letter in the same column (~~0.05). Data are from Kanach /I Oi. * where
Overall
Color
Cowpea level (‘%J) 0
2.89 a
were not significantly
different
The energy and manpower requirements for the process were estimated and are presented in Table 4. It is noted that the electric ~eqnireInent for extrusion was much higher than the average value of commercial processes, which is about ML 4 - Cl.2 kW l&g product 1131.One of the reasons could be due to the small experimental state. Further ~nvest~gatj~~~ is needed to verify the inforl~at~ot~.
Potato slices were chosen as a mode! food system fo ~re~e-~~. White potatoes, c&ivar Russet ~~rk~ta~~,c~~~ta~~~~n~ about 82% moisture were cut into 6.3 mm slices, jndiv~~~a~~~quick frozen. and stored at -40 ‘YI. A ~~~trogenat~nos~~~erewas used at the lowest prcssurc 267 Pa achieved by the freeze dryer to a~~r~~c~ conditions on the Moon, Carbon dioxide ~~ainta~nedat 773 Pa was used to simulate a Martian atmosphere. A Labconco freeze dryer with a heat rack was modified by attaching a gas inlet valve to a port on the drying chamber. For each observation, approximately 100 g of potatoes were accurately weighed and placed on the heat rack in the drying chamber. The chamber was evacuated, filled with the desired gas (nitrogen or carbon dioxide), and evacuated again, insuring that the drying occurred in the desired atmosphere. The pressure level of the simulated at~~ospl?~~ein the chamber was ~~onitored by a millitorr meter. For observations at 173 Pa, the gas valve was sl~~~t~~opened tn allow the chamber to ~~~ai~~tajn the required pressure. For observations at the higher plate temperature (33”C), heat pfzz&eswere first turned or? two hours after drying began to prevent melting and collapse of the product. After the specified drying time, the vacuum was broken with the desired gas. The slices were removed and weighed to crilculare the remaining moisture content.
Free~e-dryillg isa viable aption frtrfcmf~rese~a~jan in a Lmar or Ma~ja~ QU~FQS~~F~g~~~I ~~~~~~6~ moisture ioss of potato slices during ~ree~e-dr~~n~at 20°C. The cririca! moisture co~~e?~tfor dried ~~~aF~ sks is about 3%. The optii~~m drying time for potato siices in a ~arbu~ dioxide at~~~~~~l~~e at XP@ is about 12 h. Tbe o~~~rn~rndry~~gtime in nitrogen is about 15 h. The difference could be due to the higher thermat co~ducti~jty in the presence of CO2 than I?2 or could be due to the v~r~ab~~ity of thermal conductivity fram one sample to another. Figure f also shows that the higher at~~os~heric pressure results iu a siower dryiug process since the higher pressure causes a smaller pressure gradient, which is the d~ivj~g force for mass transfer during ~~~~~e-d~~~g. Using heat&g plates at 43°C greatly reduced the ~~~i~~~Gne at 267 Pa. However, heating at 43Y Ied to ~~e~ti~~g for both a carbon dioxide and a i~jtro~~~atmosphere of 733 Pa. A small amount o~bro~~~~~gon the surface was observed from the
( 1111248
.
_____
267 Pa
CO2
773 Pa
CO2
267 Pa
N2
773 Pa N2 __. ..
Freezing time (hr)
Fig. I. Freeze~dryitl~ curves ofpotato slices in simuIated space conditions with the heating plate temperature of’ 20 OC ll~j~-b~a~c~ed potato slices. ‘This could be either enzymatic or f~~~~~e~l~~~l?atic or both. Further work is being undertaken to study the effect of freeze-drying on food quality under simulated space conditions. Product characteristics. such as vitamin C content. color. pi-f, texture. and rehydrat~on ratio are being studied.
Oil is the most coI~~e]~trated form of ef~ergy-produ~ii~g nutrients. Oil may be used directly in food preparation or as an iI~gredi~]~t in food products made from CELSS crops. Oil extractjon is an i~npot~a~~t step for utilizing oilseeds. The current commercial process to extract oil is not suitable for the CELSS e~?viro~~I~e~~tsince it involves a flammable organic solvent, hexane. Mechanical extraction of oil normally involves a ~ornbiilatiol~ of seed preparation and heating and expelling processes, Processir~g col~ditiolls will he d~c~ted by oil quality and protein quality of the press cake as well as e~trac~io1~ efficiency. The col~rnoi~ly recognized disadvantage of tow extraction ef~ciellcy may not be a problem for a CELSS sincethe press cake will be further processed for human consumption and will be as important as the oil. Characteristics of the low-fat cake from oil pressing need to be studied, and its utilization in various food systems needs to be investigated. New alternative food processing methods or novel CojnbiI~atiol~s of existing methods are ~;~~~~jnuall~ being illvesti~ated in the pursuit of producing better quality foods more e~onorni~ali~. S~lper~ritical fluid extraction is sucl~ a process that may also be used to extract oil from oiiseeds /‘I 9, An important feature in favor of supercritical extraction is the possibility of using a ilo~~~a~~~tnabi~ and innocuous medium. forexaI~pie CO2. At pressures above 30 MPa and at telnperat~lr~s between 60 and WC, seed oils are fairly soluble in compressed COz. The dissolved oil is free from pllosphatid~s. This process can be combined with the mechanical oil pressing discussed above. The residual oii in the resultant press could be treated with supercritical CO2 as a further procedure. ~esoivei~ti~~ is urmecessary because the compressed gas rapidly escapes from the cake once processing has ended. Carbon dioxide under pressure can also kill bacteria, molds, and yeasts. The effect could be s~ll~rgisti~ with raised temperature and acidic pH and antagoll~ed by lowered water activity.
PmesstngCEL.S Foe&
f1/2Y%49
High hydrostatic pressure is another new process that may be used to inactivate microorganisms in certain foods or food ingrediel~ts /I&‘. The appJi~ation of hydrostatic pressure is uniform and i~~stantaneoustl~rougho~~ta food. It is unique in that the effects do not fotlow a concentration gradient. A ~ornbinatjol~ with other metilods may be necessary since most bacteriaf spores are scarcely affected by pressure and enzymes are also quite resistant. They may have to be inactivated by heat. Nowever, different foods react differently to pressure in their flavor, texture, and color responses with ~~rr~s~oi~djn~Jy different storage effects, The type of foods most likely to benefjt from this novel processing. especially in the CELSS ~~~viro~rnent~remain to be jdentj~ed and deveioped. This te~J~~~~Jo~~ may aEso End a~~~j~at~onin other subsystems~ such as waste ~~atrne~t ~su~er~rjt~~aiwater oxidation), and plant growth (sterilization of nutrient medium). T~~bnoJogy advances are needed before it can actmlly be utilized. An aqueous extraction method may be employed as an alternative oilseed milling process to extract oil, protein and starch sit~~ulta~le~usl~1171.Ohmic heating, osmotic drying, and modified and controlled atmosphere J~a~kagil~~may also be emptoyed for CELSS purposes. However, more research is definitely needed to identify the type of foods that can benefit from these processes in the CELSS environment.
How to produce nutritious, safe, pala~abJe. and versatile foods from a limited source of bjo~~ss materi&, with serious ~o~lstraiilts in space and facilities for food processing and ~re~aratjoll, will continue to challenge food scientislsiengineers. Research efforts are needed at least in the folJow~~~g areas: (1) Further j~lvestigatiol~of adaptability of ~o~~~~F~o~~~ food ~rocessjfl~ operations to the space el~vir~~ilrn~nt~ (2) developmei~t of novel gravity-il~sellsitive professing systems; (3) potential appii~ations of space resources; (4) utilizations of I~oIl-traditional plant biomass or food sources for both food or nonfood purposes. which ~311play 3 key roie in reducing the Joad for recpcting and regeneration in 3 CEIS. For esamplc, food ~l~~redi~l~ts such as glucose and vinegar, may be ohtamed from waste recovery, which may be used in n~al~u~~ct~~rj~~~ engineered foods or other food products. Progress in otJ%erareas, such as plant ~~~du~tjo~?,genetic e~~~i~~eerin~, waste Trident, and autol~atjo~~ may also impact the design of the food processing s~lbsystem for a CELSS Some plant ~hara~ter~stj~s~ such as harvest index and piant ~o~~pos~t~o~~, can be jm~roved by geer-retkl~odj~~atjo~?or o~t~rn~~atjol~ of growing conditions, For example. a dwarf eanoJa rapeseed is being d~~eJoped by genetic et~g~~e~rii~~ 1%. If the urucic and gJ~~osil~atescan be reduced suf~ci~~ltl~~,then both the oil aud the cake could be used far human co~lsu~n~tioI1directly without any addit~oI~a~processing steps. Another example would he to genetically remove the liposygenase, which is responsible for the beany tlavor in many bean products /IX/. This will not only improve the quality but may also lessen the processing requirements. ‘The de~el~~~~~~~~~t of ~~~teJli~e?~t robots wilt de~n~teJ~ liberate l~urna~sand ill~lue~~~ethe design of food processing hardware. In additjo~~,~o~lt~~~~~s~~ research on human phys~oio~~~aJresponses to the Jobs-term space ~~~~;i~~~~~~i~~ will certainly lead to better und~rstandin~ of human I~utr~t~onaJ reqn~r~~~e~~s.thus jn~~u~~~cjl?~ meal pre~arat~ol?.There is much to be done before food ~roc~ssin~ can occur Jn space.
3. SM. Schwartzkopl%, Design of a controhed ecological life support system, ~~~~,~~~~~~g. Q (7). 526-535 {1992). 4. i& KareJ and AR. Kamare~, ~easjb~~~tyof~rodu~~~?ga range of food products from a Jii~~~edrange of ~~~d~ffereI~tiated major food ~~rnp#~~~ts~ NASA CR- I77329, I t 984).
8. Fu et al.
(In)zFo
5. M. Karei and Z. Nakhost, Utilization of non-conventional components, NASA CR-I 77545, (1989).
systems for conversion
6. Z. Nakhost and M. Karel, Utilization of non-conventional components. NASA CR- 177449, (I 986).
systems for conversion
of biomass to
food
of biomass to food
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and constraints
offood
durum wheat, J.
processing in space. Food ~~~~~~~~~, (in
print). 10. L.L. Kanach.
Extrusion
of Durum Semolina
M.S. thesis, Purdue University,
W. Lafayette,
Substituted with Cowpea and Assessment of Quality,
IN. (1993)
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IN. f 199 I ).
12. R. Irvine, K. Cooksey, and FE. Nelson, Feasibility of freeze dellydration under lunar and Maniacs conditions, presentated at the Institute of Food Technologists Annual Meeting, June 25-29, Atlanta, GE. (1994). 13. J.M. Harper. Food extrusion,
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14. D.M. Bird, G.E. Seely. C.L. Miller, D.E. Sandlin, M.R. Yakely, A.C. Gomillion. and P.J. Holland, Harnessing the resources space in the recovery of potable water from waste water by Iyophilization, 23rd International Conference on Environmental Systems, Colorado Springs, CO. ( 1993).
of
16. R, Eggers and U. Sievers, Processing of oilseed with supercriti~al Jupun, a
carbon dioxide,
f. ~~~~. EBB
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alternative
oilseed milling
18.C.S. IJavies, S.S. Nielsen, and N.C. Nielsen, Flavor improvement 64(IO), 1428-1433 (1987). of liposygenase--, 3 s/4oc-s, .
ofsoybean preparations
by genetic
removal
Journal Series Paper No. 14345 from the Purdue Unjversity is partially supported by NASA grant NAGW-~~29-
Agricultural
experiment
Station. This work