| Coffee pulp is one of the main by-products in coffee bean production,and its low utilization rate leads to serious environmental pollution and resource waste.Coffee pulp is rich in nutrients and dietary fiber,so it has been processed into coffee pulp tea and used in baked goods in recent years.Roasting not only affects the chemical composition,flavor,and quality of food products,but also produces some harmful Maillard reaction products（MRPs）such as 5-hydroxymethylfurfural（5-HMF）andα-dicarbonyl compounds（α-DCs）.Therefore,studying the effects of roasting process on the physical and chemical properties,flavor,and harmful MRPs of coffee pulp will help to develop high quality coffee pulp teas and baked goods.The present research first investigated the effects of roasting conditions on drying characteristics,chemical composition,antioxidant activity,and flavor of coffee pulp,and screened the optimal roasting conditions for coffee pulp.Secondly,coffee pulp was added to cookies,and the effect of the amount of coffee pulp on the quality of cookies.The optimal amount was determined through sensory evaluation,and then the quality and flavor of cookies without and with sun-dried or roasted coffee pulp added were compared.Finally,the physical,chemical,flavor,and microbial changes of three types of cookies during storage were studied using the accelerated shelf-life method testing method.The main findings were as follows:（1）The drying rate of coffee pulp conforms the logarithmic kinetic model.Proper roasting temperature and time can increase the total phenolic content（TPC）and antioxidant activity of coffee pulp.Although roasting significantly reduced the content of chlorogenic acid（5-CQA）in coffee pulp,its antioxidant activity increased,which may be related to the production of the late-stage MRPs.The degradation rate of 5-CQA was positively correlated with the roasting temperature,and the degradation of 5-CQA and changes in color indices（L*,a*,b*）conformed the first-order kinetic model.Monosaccharides,disaccharides,and amino acids in coffee pulp decreased with increasing roasting degree.Roasting deepened the browning of coffee pulp as well as increased the content of 5-HMF andα-DCs（GO and MGO）.The generation rate of 5-HMF conformed to the zero-order kinetic model.At a roasting temperature of 160℃for 6 min,coffee pulp has high TPC and antioxidant activity as well as a low content of harmful MRPs.Therefore,this roasting condition is selected as the preferred roasting condition.（2）Electronic nose analysis revealed that sulfur compounds were the main aroma components in coffee pulp,and prolonged roasting can significantly reduce the content of sulfur compounds,while nitrogen oxides increased with the degree of roasting.Using headspace solid-phase microextraction gas chromatography（HS-SPME-GC-MS）,106 volatile compounds（VOCs）were identified in sun-dried coffee pulp（SCP）,while 129 VOCs were detected in roasted coffee pulp（RCP）.Among them,79 substances were common to both samples,27 VOCs were only present in SCP,and 50 VOCs were only present in RCP.Through multivariate statistical analysis,83 differential volatile compounds were screened,45 compounds increased and 38 compounds decreased after roasting.Esters showed the greatest change in quantity before and after roasting,followed by acids,furans and ketones.The number of acids decreased,while and the number of esters,furans and ketones increased.Odor activity value（OAV）analysis showed that before roasting coffee pulp had a fresh,grassy,and floral aromas,while after roasting,the fatty,creamy,and caramel aromas increased.（3）Coffee pulp significantly increased the water-holding and oil-holding capacity of the flour.With the increasing addition of coffee pulp,the color of cookies deepened,and the hardness and chewiness decreased,while the viscosity increased,and elasticity showed a trend of first decreasing and then increasing.Coffee pulp significantly increased the TPC,antioxidant activity,5-HMF content,and ash content of the cookies,while decreasing the moisture content.The sensory evaluation score of the cookies was the highest when the addition of coffee pulp was 5.0%.Electronic nose analysis showed that coffee pulp cookies contained nitrogen oxides,short-chain alkanes,and sulfides,and both nitrogen oxides and sulfides gradually increased with the increase of coffee pulp.Using HS-SPME-GC-MS,93,92,and 100 VOCs were identified in the control cookies（without coffee pulp）,cookies with sun-dried coffee pulp（SCPC）,and cookies with roasted coffee pulp（RCPC）,respectively.The addition of coffee pulp increased the number of heterocyclic,ketones,hydrocarbons,and alcohols,but decreased the number of esters in cookies.The control group contained higher levels of 2-nonanone,butyric acid,acetic acid,3-furaldehyde and2-methylpyrazine,while the cookies with added coffee pulp contained higher levels of hydroxyacetone,2-nonanone,acetic acid,3-furaldehyde,and 2-methylpyrazine.Hexanal was the key differential VOCs to distinguish SCPC and RCPC.OAV analysis revealed that the control group cookies showed fatty,grassy,fruity and sour flavors,while the coffee pulp cookies had sour,fatty,grassy and caramel flavors.（4）Studies on the accelerated shelf-life method have found that the hardness and chewiness of cookies increased with storage time and temperature,while elasticity gradually decreased.As storage time and temperature increase,the rate of lipid oxidation accelerated.Adding coffee pulp to cookies can inhibit lipid oxidation,and the inhibitory effect became more significant with the increasing temperature.The color index L*of the three types of cookies increased during storage,while and a*and b*decreased.With the increase of storage time,sulfide,nitrogen oxide,short-chain alkanes,alcohols,aldehydes,and ketones in cookies showed a trend of first decreasing and then increasing,while the content of long-chain aliphatic alkanes gradually decreased.At 35℃,the flavor of cookies began to change to varying degrees from the 4thday,and there was a significant difference on the 40thday,while cookies with added coffee pulp could better retain nitrogen oxides and sulfur-containing inorganic compounds,and terpenoids.No coliforms were detected in coffee pulp cookies at any of the three storage temperatures,while the total number of colonies and molds increased with storage time,and cookies with added coffee pulp showed better antibacterial effect than the control group.The microbial content of all cookie samples met the national regulations. |
