Loren Dowd 10/6/15 Lab Report: Glucose Content & Maillard Reactions in Fried Potatoes Introduction: Maillard reactions are browning reactions that occur in foods that are not primarily sugar when they are heated. Sugar molecules combine with amino acids to form brown pigments that contribute to the “browned flavor” we associate with cooked foods like grilled meats, browned baked goods, and fried potatoes. These reactions are an important part of cooking for both home and professional chefs. Because the reactions depend on sugar and amino acid quantities, foods with different levels of each will brown differently and have their own unique flavors. Taking a look at a common food, in this case potatoes, gives insight into how sugar content can affect browning reactions. Storing starchy foods at different temperatures can result in different sugar levels, due to starch to sugar conversions, which will ultimately affect their appearance once cooked. Understanding the effects of temperature on sugar content of potatoes and the subsequent browning through Maillard reactions has a practical application in the modern world of food processing, in which we preserve many of our foods by freezing or refrigerating them before cooking. It is important to understand the effects these temperature changes may have on the chemical structure of foods, and how that affects their cooking. Purpose: To observe the effects of storage condition temperature on the glucose content of potatoes, and how glucose content affects the amount of browning when fried. Hypothesis: Potatoes stored at colder temperatures will contain larger amounts of glucose because a decrease in temperature increases starch to sugar conversion. The potatoes with higher glucose content will brown more because Maillard reactions take place between sugars (glucose) and amino acids, and that greater amount of sugar will increase Maillard reactions and cause more browning. Materials: One bag of potatoes (6 or so), split in half and stored at different conditions A glucometer & test strips A deep fryer (Or a deep pan and canola oil) Food processor or blender Tongs Paper towels Baking sheets Bowls and plates Procedure: 1. Store potatoes for 1-2 weeks in three groups: one at 0˚C/30˚F (frozen), one at 4˚C/40˚F (refrigerated), and one at 21˚C/70˚F (room temperature) – all in the
Transcript
Loren Dowd 10/6/15
Lab Report: Glucose Content & Maillard Reactions in Fried Potatoes
Introduction:
Maillard reactions are browning reactions that occur in foods that are not primarily sugar when they are heated. Sugar molecules combine with amino acids to form brown pigments that contribute to the “browned flavor” we associate with cooked foods like grilled meats, browned baked goods, and fried potatoes. These reactions are an important part of cooking for both home and professional chefs. Because the reactions depend on sugar and amino acid quantities, foods with different levels of each will brown differently and have their own unique flavors. Taking a look at a common food, in this case potatoes, gives insight into how sugar content can affect browning reactions. Storing starchy foods at different temperatures can result in different sugar levels, due to starch to sugar conversions, which will ultimately affect their appearance once cooked. Understanding the effects of temperature on sugar content of potatoes and the subsequent browning through Maillard reactions has a practical application in the modern world of food processing, in which we preserve many of our foods by freezing or refrigerating them before cooking. It is important to understand the effects these temperature changes may have on the chemical structure of foods, and how that affects their cooking. Purpose:
To observe the effects of storage condition temperature on the glucose content of potatoes, and how glucose content affects the amount of browning when fried. Hypothesis:
Potatoes stored at colder temperatures will contain larger amounts of glucose because a decrease in temperature increases starch to sugar conversion. The potatoes with higher glucose content will brown more because Maillard reactions take place between sugars (glucose) and amino acids, and that greater amount of sugar will increase Maillard reactions and cause more browning. Materials: One bag of potatoes (6 or so), split in half and stored at different conditions A glucometer & test strips A deep fryer (Or a deep pan and canola oil) Food processor or blender Tongs Paper towels Baking sheets Bowls and plates Procedure:
1. Store potatoes for 1-2 weeks in three groups: one at 0˚C/30˚F (frozen), one at 4˚C/40˚F (refrigerated), and one at 21˚C/70˚F (room temperature) – all in the
dark. Make sure they are of similar size/from the same bag of potatoes, so as to eliminate as many variables as possible. Keep these groups separated throughout the experiment.
2. Peel the potatoes, cut them into wedges/sticks as desired, and set aside three or four pieces of each group for sugar analysis.
3. Fry the rest in 350˚F oil for 8 minutes or until done. Qualitatively evaluate the potatoes for browning, texture, and taste.
4. Take the three or four pieces of potato from each temperature group and extract the liquid by blending them in a food processor or blender until there is enough liquid for a glucose test strip to read.
5. Use the glucometer to take a glucose reading of each potato group three times, record these numbers, and average them.
6. For additional analysis, mash a cooked potato stick from each group with a tablespoon of water, and take a glucose reading.
7. Determine which storage temperature resulted in the highest number of reducible sugars, and see how the taste and appearance (browning) are affected.
Data:
Storage Type Time period Glucose Content (mg/dL) | Averages
Overall Appearance Taste & Texture
Room Temperature (23˚C)
Before cooking
37 79 (Avg of second two: 101)
•Edges browned •Were crispy on outside •Fully cooked all the way through
•Taste like French fries that we’re used to – very potato-y •Cooked but still firm
112 89
After cooking 36 39 41
Refrigerated (8˚C)
Before cooking
168 169 •Soaking up more oil than room temperature •Crispy outsides •Lightly browned
•Taste the best – good quality French fries •Fluffy insides
175 164
Refrigerated after cooking
92 99 96 108
Frozen (1˚C) Before cooking
66 122 (Avg of second two: 150)
•Much browner than room temperature •Soaked up more oil •Grayish coloring
•Tastes like cardboard •Less potato taste •Very soft on inside but crispy on outside •Small ones are better tasting
138
161 Frozen after cooking
116 114 111
Observations during liquid extraction & cooking: [Do not have for refrigerated group] Room Temperature
• 2:10 min first saw browning • 5 min - turned up heating - hypothesize that not hot enough to complete browning
o may be cooked through before browned • 6 min - cooked, brown on edges • 8:30 min - pulled all fries, think oil not hot enough
Frozen
• when blended, more water content • soaking up more oil? translucent • 5 min - pulled one, not cooked • 7 min - brown • 8 min - looks like fry
Results: Before starting, we measured the temperature of the three locations we had stored potatoes: the kitchen (room temperature), the refrigerator, and the freezer.
Two group members extracted liquid from the potatoes of each group, one at a time, and measured its glucose level, as the other group members cooked the potatoes of each group in the same order. The room temperature potatoes came first, then frozen, then refrigerated. For the low glucose readings on room temperature and frozen potatoes (the first ones listed for each in the data table above), the glucometer test strip was stuck into the potato (we were experimenting to see which method worked best). For the rest of the readings, the test strip was stuck into the liquid produced by blending.
The potatoes that were stored at room temperature produced the least liquid when blended, but the average of 3 glucose readings from this liquid was the lowest of the three test groups. These potatoes browned in the hot oil, but only around the edges and not as much as those from the other two groups, and tasted like normal French fries. They took about 8 minutes to fully cook, though they were still firm on the outside, and we set this as the standard cooking time for all the groups.
The frozen potato sticks had a glucose content that was between the refrigerated and room temperature levels. When blended, they produced the most liquid, which made testing the glucose level easier. During cooking, the sticks seemed to absorb a lot of oil and began to look a bit gray and translucent. This appearance stuck around through the cooking and after they were pulled from the oil. They browned more than the room temperature ones, but they had no potato taste, and one group member described them as “tasting like cardboard.”
The refrigerated potatoes had the highest glucose content of the three test groups. When cooked, they soaked up more oil than the room temperature potatoes and had crispy outsides. They still had fluffy insides and tasted the most like high quality French fries. After 8 minutes, they were fairly browned on multiple sides.
Taking glucose readings of the cooked potatoes was meant to fulfill our curiosity and further test sugar use in Maillard reactions. The glucose levels of the cooked potatoes from each temperature group were lower than their initial ones, though we did have to mix water in with mashed cooked potato to get successful readings.
Left: Setup for cooking the potatoes in an inch of Canola oil heated to 350˚F in a cast-iron skillet. Right: Refrigerated potato group after cooking.
Comparison of a potato stick from each temperature group. Refrigerated potatoes had the least browning, room temperature had even browning, and frozen potatoes had browning in addition to a translucent grayness.
Conclusion & Discussion: The refrigerated and frozen potatoes had higher average glucose contents than the room temperature ones (169 mg/dL & 150 mg/dL compared to 101 mg/dL), as measured by the glucometer, which aligns with my hypothesis. The colder temperatures at which these potatoes were stored influenced greater starch to sugar conversion, resulting in higher sugar (glucose) content. Unexpectedly, the frozen potatoes had a lower glucose content than the refrigerated ones. Temperature and sugar content of foods have an inverse relationship, so a drop in temperature should have resulted in an increased amount of sugar. One possible explanation for the frozen potato glucose level being below that of the refrigerated one is that blending the frozen potatoes seemed to melt them, so their temperature when we took the glucose reading was not the temperature at which it was being stored. Their glucose level was still above that of room temperature though.
Both the refrigerated and frozen potatoes browned considerably after 8 minutes in the hot oil, while the room temperatures ones showed very little browning. In line with my hypothesis, this makes sense because higher sugar content would increase the number of sugar molecules available for Maillard reactions, and increased reactions would produce more product, which is responsible for the browning. There is some uncertainty concerning the amount of browning that occurred because we did not cook the potatoes from each temperature group in one batch. We cooked the room temperature, then frozen, then refrigerated potatoes, and there is a possibility that the oil got hotter over time. It may not have been as fully heated when the room temperature potatoes were cooked, resulting in less browning. The frozen and refrigerated potatoes also seemed to absorb more of the oil, taking on some translucence, the frozen potatoes even taking on a grayish color in some areas. Perhaps they soaked up more oil because it was at a higher temperature.
Overall, the potatoes did not brown as much as we expected, though this may have been a consequence of pan frying instead of deep frying, the type of oil, and whether or not the oil was heated to a sufficient temperature. The original lab that this was based on notes that less browning in the room temperature potatoes is possibly the more desirable option. The larger context for this implies that the colder temperatures at which we store potatoes for preservation may be causing excess browning during cooking, which may not be as visually appealing.
In our case, it seems that the refrigerated potatoes resulted in the highest quality fried potatoes, with the most even browning. The room temperature potatoes were not as soft on the inside, though this may have been due to the lower temperature oil. The original lab seems to indicate that storing potatoes at room temperature produces the best results, as may have been the case if we’d cooked the three groups of potatoes together.
The information we have gained from this lab, though subject to some error, has the potential to inform us about the ways in which the temperature at which we store foods can have an effect on the cooked appearance, flavor, and texture of those foods. Many of the foods at fast-food or chain eateries are delivered having been flash frozen and pre-cut or pre-prepared in some way. Doing experiments such as this one help us figure out whether and how this may be having an effect on the content and quality of our food. The lack of quality seen in our frozen-then-fried potatoes, with their gray color and soaked-up oil, seemed to indicate that cooking potatoes from frozen may not be the best
option when attempting to produce quality products. This could have an impact on the way that food preparation is conducted. It is evident that food storage temperatures do have an effect on the chemical structure of foods—breaking down starches in to sugars, to name one effect—and that this in turn has an effect on the way the foods behave when cooked. Labs referenced in preparation and lab write up:
