Process for the production of thermally modified starch

Abstract

Process for the production of thermally modified starch comprising the steps of mixing starch in powder form having a specific moisture content with an alkaline water solution to obtain a wet powder; feeding a continuous flow of said wet powder into a continuous dryer together with a continuous flow of hot air; discharging a continuous flow of dried powder from said continuous drier; supplying said continuous flow of said dried powder into a turbo-reactor, in which the inner wall of said turbo-reactor is maintained at a specific temperature; converting said dried powder into a thermally inhibited starch; and discharging said thermally inhibited starch from said turbo-reactor; it is also disclosed a thermally inhibited starch obtained from the aforementioned process with enhanced physical chemical properties.

Claims

1. A process for continuous modification of starch, comprising the steps of: a) mixing starch in powder form having a moisture content between 9% wt and 25% wt with an alkaline water solution to obtain a wet powder; b) feeding a continuous flow of said wet powder into a continuous dryer together with a continuous flow of hot air, said flow of hot air having a temperature between 100 C. and 160 C. to obtain a continuous flow of dried powder; c) discharging said continuous flow of dried powder from said continuous drier, said dried powder having a moisture content between 2% wt and 4% wt; d) providing a turbo-reactor comprising a cylindrical tubular body having at least one inlet opening for the introduction of said continuous flow of dried powder and at least one discharge opening, a heating jacket for bringing the temperature of said cylindrical tubular body to a predetermined temperature and a rotor, disposed in the cylindrical tubular body and comprising a shaft provided with elements projecting radially from it; e) supplying said continuous flow of said dried powder into said turbo-reactor, in which the inner wall of said turbo-reactor is maintained at a temperature between 150 C. and 250 C. by means of said heating jacket and the rotor is rotated at a speed greater than or equal to 800 rpm, so that said dried powder is continuously centrifuged and advanced inside said turbo-reactor through the action of said rotor for a time between 4 minutes and 7 minutes and converted into a thermally inhibited starch; f) discharging said thermally inhibited starch from said turbo-reactor.

2. The process according to claim 1, wherein said step e) is carried out maintaining said dried powder at pH between 8.5 and 9.5.

3. The process according to claim 1, wherein said step a) is carried out by means of a continuous mixer.

4. The process according to claim 1, wherein in said step b) said continuous flow of said wet powder is continuously fed to a turbo-dryer comprising a cylindrical tubular body having at least one inlet opening, for the introduction of said wet powder, one air-inlet opening for the introduction of said continuous flow of hot air and at least one discharge opening for discharging said continuous flow of dried powder, a heating jacket for bringing the temperature of said cylindrical tubular body to a predetermined temperature and a rotor, disposed in said cylindrical tubular body and comprising a shaft provided with elements projecting radially from it, being the inner wall of the turbo-dryer maintained at a temperature between 150 C. and 180 C. by means of said heating jacket and the rotor being rotated at a speed greater than or equal to 800 rpm, said continuous flow of wet powder being continuously centrifuged and advanced inside said turbo-dryer through the action of said rotor.

5. The process according to claim 4, wherein step b) is carried out for a time between 15 seconds and 120 seconds.

6. The process according to claim 4, comprising the further steps of: g) supplying a continuous flow of said thermally inhibited starch into a further turbo-reactor which comprises a cylindrical tubular body having at least one inlet opening for the introduction of said thermally inhibited starch and at least one discharge opening, a heating jacket for bringing the temperature of said cylindrical tubular body to a predetermined temperature and a rotor, disposed in the cylindrical tubular body and comprising a shaft provided with elements projecting radially from it, in which the inner wall of the further turbo-reactor is maintained at a temperature between 150 C. and 250 C. by means of said heating jacket and the rotor is rotated at a speed greater than or equal to 800 rpm, said thermally inhibited starch being continuously centrifuged and advanced inside said further turbo-reactor through the action of said rotor, in order to further enhance starch thermal inhibition; h) discharging said thermally inhibited starch from said further turbo-reactor.

7. The process according to claim 6, wherein said step g) is carried out for a time between 4 minutes and 7 minutes.

8. The process according to claim 1, wherein said flow of alkaline water solution comprises a base, said base having a pKb between 1 and 13.

9. The process according to claim 8, wherein said base is a food grade additive, said base being selected from an element of the group consisting of dibasic oxalate metal salt, dibasic tartrate metal salt, tribasic citrate metal salt, tribasic phosphate metal salt, monobasic carbonate metal salt, dibasic carbonate metal salt, glycinate metal salt, calcium hydroxide and any combination thereof.

Description

(1) The advantages and characteristic features of this invention will emerge more clearly from the detailed description, provided below as a non-limiting illustration of a preferred embodiment according to the present invention, with reference to the apparatus schematically shown in the attached FIGURE.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

(2) With reference to the FIG. 1, an apparatus used for the process according to the invention comprises a continuous mixer M consisting essentially of a cylindrical tubular body 1, closed at the opposite ends by end plates 2, 3.

(3) The tubular body 1 is provided with inlet openings 5, 6 respectively for the organic substrate (starch) and for the alkali aqueous solution, and with a discharge opening 7.

(4) The tubular body 1 rotatably supports internally a rotor comprising a shaft 8 provided with elements 9 radially projecting therefrom in the form of blades, these blades 9 being arranged helically and oriented so as to centrifuge and at the same time convey towards the discharge outlet 7 a flow of wet powder resulting from mixing the aforementioned two flows.

(5) A motor not shown is envisaged for operation of the bladed rotor at variable speeds, which can be greater than or equal to 800 rpm.

(6) When it exits from the continuous mixer M, the aforementioned wet powder is continuously fed via a pipe 11, in fluid communication with the discharge opening 7 of the continuous mixer M, to the turbo-dryer D through the inlet opening 105.

(7) The turbo-drier D consists essentially of a cylindrical tubular body 101, closed at the opposite ends by end plates 102, 103 and coaxially provided with a heating jacket 104 intended to be passed through by a fluid, for example diathermic oil, so as to keep the inner wall of the body 101 at a predefined temperature.

(8) The tubular body 101 is provided with an inlet opening 105 for the introduction of the aforementioned wet powder discharged by the discharge opening 7 of the continuous mixer M. The inlet opening 105 of the tubular body 101 of the turbo-dryer D is in fluid communication with the discharge opening 7 by means of the pipe 11.

(9) The tubular body 101 is provided with an air-inlet opening 106 for the introduction of a flow of hot air inside the tubular body 101 of the turbo-dryer D. The air-inlet opening 106 is in fluid communication with a conventional air-heating system which is not part of the plant according to the present invention and/or is in fluid communication with a conventional reservoir for the storage of hot air which is not part of the plant according to the present invention and/or is in fluid communication with the atmosphere.

(10) The tubular body 101 is also provided with a discharge opening 107.

(11) The tubular body 101 rotatably supports internally a rotor comprising a shaft 108 provided with elements 109 radially projecting therefrom in the form of blades, these blades 109 being arranged helically and oriented so as to centrifuge and at the same time convey towards the outlet 107 the flow of hot air and wet powder.

(12) The wet powder entering the turbo-dryer D is centrifuged by the blades 109 of the rotor against the inner wall of the cylindrical tubular body 101, heated by means of the heating jacket 104 and by the aforementioned flow of hot air to a temperature between 150 C. and 180 C., preferably between 160 C. and 170 C.

(13) The discharge opening 107 is used to discharge a continuous flow of hot air and water vapor, which can be released into the atmosphere or to a system for heat recovery, and a flow dried powder, resulting from drying of the aforementioned wet powder following the heat exchange of the latter with the wall of the turbo-dryer heated by the heating jacket 104 and with the flow of hot air.

(14) Therefore, the continuous flow of dried powder discharged from the discharge opening 107 of the turbo-drier D is continuously fed, via a pipe 111, into the turbo-reactor T, through the inlet opening 205.

(15) The turbo reactor T consists essentially of a cylindrical tubular body 201, closed at the opposite ends by end plates 202, 203 and coaxially provided with a heating jacket 204 intended to be passed through by a fluid, for example diathermic oil, so as to keep the inner wall of the body 201 at a predefined temperature.

(16) The tubular body 201 is provided with at least one inlet opening 205 for the introduction of the aforementioned flow of dried powder discharged by the discharge opening 107 of the turbo-dryer D. The inlet opening 205 of the tubular body 201 of the turbo reactor T is in fluid communication with the discharge opening 107 by means of the pipe 111.

(17) The tubular body 201 is also with a discharge opening 207.

(18) The tubular body 201 rotatably supports internally a rotor comprising a shaft 208 provided with elements 209 radially projecting therefrom in the form of blades, these blades 209 being arranged helically and oriented so as to centrifuge and at the same time convey towards the outlet 207 the flow of material contacting them.

(19) The wet powder entering the turbo-reactor T is centrifuged by the blades 209 of the rotor against the inner wall of the cylindrical tubular body 201, heated by means of the heating jacket 204 to a temperature comprised between 150 C. and 230 C.

(20) The rotation of the shaft 208 of the bladed rotor at a speed at least greater than or equal to 800 rpm has the effect that a dynamic, thin, tubular layer of the aforementioned wet powder is created against the heated inner wall of the cylindrical tubular body 201 and an intense heat exchange takes place between the mixture and the aforementioned inner wall.

(21) The resulting thermally inhibited starch is then continuously discharged from opening 207 of the turbo-reactor and then is continuously fed, via a pipe 211, into a continuous further turbo-reactor T, through the inlet opening 305.

(22) The further turbo-reactor T, which has a structure entirely similar to that of the aforementioned turbo-reactor T, is not described in detail. The components of the further turbo-reactor T, which are the same as those of the turbo-reactor T, are indicated by the same reference numbers increased by 100.

Example 1

(23) A flow of waxy corn starch in powder form with a moisture content of 13.77% was continuously fed (150 kg/h), through the inlet opening 5, into the continuous mixer M, inside which the bladed rotor 8 was rotated at a speed of 1000 rpm.

(24) At the same time a flow of alkaline water solution, corresponding to about 6.4% w/w of sodium carbonate (Na.sub.2CO.sub.3), was continuously fed (12.8 kg/h) through the inlet opening 6.

(25) Immediately at the inlet of the continuous mixer M, the flow of starch was mechanically dispersed into particles which were immediately centrifuged.

(26) At the same time, the alkali water solution, fed through the inlet opening 6, was centrifuged by the blades of the rotor 8 in order to intimately mix it with the above flow of starch.

(27) After an average residence time of about 30 seconds inside the reactor, a wet powder with a moisture content of about 19.6% was continuously discharged from the opening 7.

(28) The wet powder thus obtained was continuously fed into the turbo-dryer D, through the inlet opening 105 with a flow rate of about 100 kg/h, in parallel with a flow of air at a temperature of about 143 C. (flow rate 285 Nm.sup.3/h), fed through the air-inlet opening 106.

(29) Inside the turbo-dryer D the wall temperature was kept at a value of 165 C., while the rotational speed of the bladed rotor 108 was kept constantly at 900 rpm.

(30) After an average residence time of 30 seconds inside the turbo-dryer D, a flow of dried powder with a moisture content of 2.85% was continuously discharged from turbo-dryer D.

(31) Then, this dried powder was continuously fed into turbo-reactor T, through the inlet opening 205, with a flow rate of 90 kg/h.

(32) Inside the turbo reactor T the wall temperature was kept at a value of about 220 C., while the rotational speed of the bladed rotor 208 was kept constantly at 900 rpm.

(33) At the inlet of the turbo-reactor T, the flow of dried powder was mechanically dispersed into particles which were immediately centrifuged against the inner wall of the reactor, where a dynamic, tubular, thin, fluid layer was formed.

(34) After an average residence of 5 minutes and 30 seconds inside the turbo-reactor, a flow of thermally inhibited starch with a moisture content of less than 1% was continuously discharged from turbo-reactor T though the opening 207.

(35) Then, such flow of thermally inhibited starch was continuously fed into the further turbo-reactor T, through the inlet opening 305, with a flow rate of 90 kg/h.

(36) Inside the further turbo-reactor T the wall temperature was kept at a value of about 220 C., while the rotational speed of the bladed rotor 308 was kept constantly at 900 rpm.

(37) At the inlet of the further turbo-reactor T, the thermally inhibited starch was mechanically dispersed into particles which were immediately centrifuged against the inner wall of the reactor, where a dynamic, tubular, thin, fluid layer was formed.

(38) After an average residence of 5 minutes and 30 seconds inside the further turbo-reactor, a flow of thermally inhibited starch, whose thermal inhibition was further enhanced and having a moisture content of less than 1%, was continuously discharged though the opening 307. The outlet temperature recorded in said flow of further thermally inhibited starch was 190 C. (starch t190).

(39) The aforementioned flow of further thermally inhibited starch was then collected and cooled to room temperature.

Example 2

(40) A flow of waxy corn starch in powder form with a moisture content of 13.77% was continuously fed (150 kg/h), through the inlet opening 5, into the continuous mixer M, inside which the bladed rotor 8 was rotated at a speed of 1000 rpm.

(41) At the same time a flow of alkaline water solution, corresponding to about 6.4% w/w of sodium carbonate (Na.sub.2CO.sub.3), was continuously fed (12.8 kg/h) through the inlet opening 6.

(42) Immediately at the inlet of the continuous mixer M, the flow of starch was mechanically dispersed into particles which were immediately centrifuged.

(43) At the same time, the alkali water solution, fed through the inlet opening 6, was centrifuged by the blades of the rotor 8 in order to intimately mix it with the above flow of starch.

(44) After an average residence time of about 30 seconds inside the reactor, a wet powder with a moisture content of about 19.6% was continuously discharged from the opening 7.

(45) The wet powder thus obtained was continuously fed into the turbo-dryer D, through the inlet opening 105 with a flow rate of about 100 kg/h, in parallel with a flow of air at a temperature of about 143 C. (flow rate 285 Nm.sup.3/h), fed through the air-inlet opening 106.

(46) Inside the turbo-dryer D the wall temperature was kept at a value of 165 C., while the rotational speed of the bladed rotor 108 was kept constantly at 900 rpm.

(47) After an average residence time of 30 seconds inside the turbo-dryer D, a flow of dried powder with a moisture content of 2.85% was continuously discharged from turbo-dryer D.

(48) Then, this dried powder was continuously fed into turbo-reactor T, through the inlet opening 205, with a flow rate of 90 kg/h.

(49) Inside the turbo reactor T the wall temperature was kept at a value of about 210 C., while the rotational speed of the bladed rotor 208 was kept constantly at 900 rpm.

(50) At the inlet of the turbo-reactor T, the flow of dried powder was mechanically dispersed into particles which were immediately centrifuged against the inner wall of the reactor, where a dynamic, tubular, thin, fluid layer was formed.

(51) After an average residence of 5 minutes and 30 seconds inside the turbo-reactor, a flow of thermally inhibited starch with a moisture content of less than 1% was continuously discharged from turbo-reactor T though the opening 207.

(52) Then, such flow of thermally inhibited starch was continuously fed into the further turbo-reactor T, through the inlet opening 305, with a flow rate of 90 kg/h.

(53) Inside the further turbo-reactor T the wall temperature was kept at a value of about 210 C., while the rotational speed of the bladed rotor 308 was kept constantly at 900 rpm.

(54) At the inlet of the further turbo-reactor T, the thermally inhibited starch was mechanically dispersed into particles which were immediately centrifuged against the inner wall of the reactor, where a dynamic, tubular, thin, fluid layer was formed.

(55) After an average residence of 5 minutes and 30 seconds inside the further turbo-reactor, a flow of thermally inhibited starch, whose thermal inhibition was further enhanced and having a moisture content of less than 1%, was continuously discharged though the opening 307. The outlet temperature recorded in said flow of further thermally inhibited starch was 180 C. (starch t180).

(56) The aforementioned flow of further thermally inhibited starch was then collected and cooled to room temperature.

Example 3 (Brabender Viscograph)

(57) The thermally inhibited starch obtained from Example 1 (starch t190) and the inhibited starch obtained from Example 2 (starch t180) were then separately characterized by means of a Micro Visco-Amylo-Graph for measuring their gelatinization properties and the viscosity values registered when mixed with water, heated to high temperature for a period of time, and the cooled to room temperature.

(58) The following procedure was carried out for starch t190, for starch t180, and for a sample of waxy corn starch, which was not subjected to any inhibition process.

(59) 12 g or dry starch was mixed with 100 g of demineralized water in a Brabender cup and placed in the measuring equipment. The Brabender temperature was set at 30 C. and the stirring speed at 250 rpm.

(60) The temperature was raised with a rate of about 3 C./min until 95 C. The mixture was kept at 95 C. for 30 min (so called cooking period).

(61) Then the mixture was cooled to 30 C. with a rate of about 3 C./min. After 1 minute at 30 C. the measurement was completed. The measuring was performed at 300 cmg.

(62) Following Table 1 shows the gelatinization properties of each starch analyzed and the viscosity registered during Brabender viscography of each starch, respectively (UB=Brabender Units, which are arbitrary).

(63) The pasting temperature is defined as the temperature at which the first detectable viscosity is measured by means of a Micro Visco-Amylo-Graph machine.

(64) The peak viscosity is defined as the highest value of viscosity attained by the mixture during the heating cycle.

(65) The cold paste viscosity is defined as the viscosity attained as the mixture (cooked paste) is cooled down to 30 C.

(66) The setback is defined as cold paste viscosity minus hot paste viscosity, wherein the hot paste viscosity is in its turn defined as the viscosity at the end of the cooking period (in the present case after having kept the mixture at 95 C. for 30 min).

(67) TABLE-US-00001 TABLE 1 Pasting Peak temperature viscosity Cold paste Setback Sample ( C.) (UB) viscosity (UB) (UB) Waxy corn 66.7 0.3 1094 1 843 14 465 3 starch t190 starch 59.8 0.1 1526 23 1090 8 347 21 t180 starch 63.4 0.1 1277 25 831 40 386 37

(68) From Table 1 it is evident that with respect to waxy corn starch, t190 starch and t180 starch both have a pasting temperature lower than waxy corn starch, which is surprisingly considerably lower for t190 starch.

(69) Starches with lower gelatinization temperature begin water adsorption and dissolution at a lower temperature and require shorter cooking time than those with higher gelatinization temperature, determining a more convenient and feasible applications, for example in formulation for the food industry.

(70) Then, one can notice that t190 starch and t180 starch allows to obtain a more viscous paste at high temperature if comparing t190 starch and t180 starch peak viscosities with waxy corn starch peak viscosity. These results demonstrate that, in mixtures comprising t190 starch and t180 starch, starch grains swell good, which means that starch has a high water-holding capacity and it is easy to be cooked: the former property is related with a better final formulation product.

(71) Then, Table 1 shows an excellent cold paste viscosity for t190 starch, which is dramatically higher than cold paste viscosity registered for waxy corn starch, and a good cold paste viscosity for t180 starch.

(72) Finally, one can notice an overall low setback viscosity of the obtained mixtures formulated with a thermally inhibited starch according to the present invention. Indeed, both t190 starch and t180 starch bring to low setback viscosity; in particular, a surprisingly low value for t190 starch is detected (347 (UB) for t190 starch compared with 465 (UB) for waxy corn starch).

(73) A low setback viscosity indicates a lower retrogradation tendency and less syneresis is likely to take place, therefore starches obtained from a process according to the present invention allow to arrive at a final product which has a better quality and shelf-life.