an Inst Food Sci Technol Vol. 22, N o. I, pp. 34-39, 989 RESEARCH A Relationship Between Colour Development and Moisture Content During Roasting o f Peanuts J.R. Moss an d L. O tt en School of Engineering University of Guelph Guelph, Ontario, Canada NlG2Wl Abstract S pl it r ed sk in p ea nu ts v ar . R un ne r) were r oa st ed in a t hr ou gh c ir cu la ti on , f or ce d- ho t- ai r b at ch r oa st er . T em pe ra tu re s v ar ie d from 7 to l7 l °C f or r oa st s of 2 to 2 min in d ur at io n. C ol ou r was m ea sur ed for all test s u si ng t he L *a *b * c o lo ur s ca le an d comp ar ed wit h t he m oi st ur e c on te nt r at io of t he n ut s. T he data sugg es t t h at a c or re la ti on e xi st s b et we en t he y el lo w- bl u e b*) c ol ou r s ca le a n d t he m oi st ur e c o nt en t r at io . Resume De s arachides a p ea u r ou ge c ass e es v ar . R un ne r) f ur en t r ot ie s dans une rotissoire en discontinu a air force a travers. Le s temperat ur es o nt v ari e de 7 a 1 71 °C p ou r des t ra it em en ts de 2 a 20 m in . Dans tous les cas la couleur f u t m es ur ee a l aide de l echelle colori metrique L*a *b * et comparee au ratio d humidite de s noix. Les donne es s ug ge re nt l existence d une c orre la ti on e nt re la c oule ur j au ne -b le ue b* ) de l ec he ll e et le ratio d humidi te. Introduction Peanuts Arachis hypogaea c ur re nt ly r an k as t he ninth most valuable cash crop in the United States with a cash value o f over o ne billion dollars. Approximately 65 1 is consumed dir ect ly as confections, peanut butter or b oi le d, r o as t ed , s al te d, or candied peanuts Woodroof,1983 ). Of these, peanut butter is the m aj or product and a cc ou nt s f or 37 1 of the domestic use of peanuts with an average annual per capita consumption o f 1.4 kg Zamula, 1985). Roasting is a critical step in peanut processing may be the most important unit process in the flavour development of peanuts and peanut butter. Roasting of peanuts can be accomplished in a number of ways. The most common commercial m et ho d used in the production of peanut butter is d ry r oa st in g bu t oil roasting is a lso use d. T he t hr ou gh -c ir cu la ti on t yp e roaster is the most widely used dry-roasting method. works on the principle of blowing hot air through a bed of p ea nu ts passing c on ti nu ou sl y t hr ou gh a chamber. Y ou ng personal communication) has done exten sive work on roaster optimization and has found that the o pt imu m process requires approximately five separate heating zones to raise the temperature o f the nuts slowly t o t he roasting t em per at ur e. H e f ou nd that peanuts roasted at lower temperatures for longer periods of time developed the best flavour due to a more even roast. The nuts also exhibited a longer shelf life due to the more even temperature distribution resulting in a higher probability of total enzyme inactivation. Drying In general, the drying process of a material may be divided into a constant-rate period an d one or more falling-rate periods. For many foods the change from constant-rate drying to falling-rate drying occurs at a w at er a ct iv it y v al ue b et we en 0. 58 an d 0 .65 E ar le , 1983). The water activity for p ea nu ts variety Runner) at an e qu il ib ri um m oi st ur e c on t en t of about 5.6 dry basis) at 25°C would be under 0.45 lglesias an d Chirife, 1982). Therefore, it is expected that the nuts coming ou t of s to ra ge a re e it he r ator near the critical point at which falling-rate drying occurs and should generally exhibit falling-rate drying char acteristi cs during roasting. The m os t widely investigated t he or et ic al drying model has been Fick s second law of d i ff u si o n. Al though it has been used to describe the falling-rate d ry in g p er io d, m a ny of the assumptions required to use this law as a drying equation for agricultural and food products have been found to be invalid. H ow ev er , e ve n w it h its i nh er en t l im it at io ns , d ry in g curves of many food products have been successful ly predicted u si ng Fick s l aw. The first term of a general series solution to Fick s law was used by Henderson and Pabis 1961) to predict the drying curve of corn: MR M-Me)/ Mo-M e ) A o exp -kot) (I ) The model was found to be accurate after one or t wo h ou rs of drying but not during the initial period. They explained that the poor fit d ring the initial stages was p ro ba bl y d ue t o t he g re at er t em pe ra tu re d if fe re nc e b et we en the kernel and the air near the Copyright 989 Canadian Institute of Food Scie nc e and Technology 34
